neotectonics of the marikina valley fault system (mvfs) and tectonic framework of structures in...

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Tectonophysics 415

Neotectonics of the Marikina Valley fault system (MVFS) and

tectonic framework of structures in northern and

central Luzon, Philippines

Rolly E. Rimando a,*, Peter L.K. Knuepfer b,1

a Philippine Institute of Volcanology and Seismology, PHIVOLCS Bldg., C.P. Garcia Ave., U.P. Campus, Diliman, Quezon City, Philippinesb Department of Geological Sciences and Environmental Studies, State University of New York, P.O. Box 6000, Binghamton,

NY 13902-6000, Science 1, 161, United States

Received 10 February 2004; accepted 23 November 2005

Available online 30 January 2006

Abstract

Recognition of neotectonic features along the Marikina Valley fault system (MVFS) in central Luzon, Philippines indicates a

dominantly dextral strike-slip motion during its most recent activity believed to be Late Pleistocene to Holocene in age. Variations in the

ratios of vertical to horizontal displacements for the segments imply a dominantly dextral motion of the West Marikina Valley fault

(WMVF) and oblique dextral motion for the East Marikina Valley fault (EMVF). The displacement data further suggest that rupturing

along the EMVF involvedmultiple segments and occurred separately from the events along theWMVF segments. Estimated earthquake

magnitudes for theWMVF and EMVF based on single-event offsets fall within the rangeM 7.3–7.7. The vertical slip component in the

northern part of the Marikina Valley is associated with the development of a basin between the EMVF and WMVF while the large

vertical component in the southernmost segment of the EMVF (Talim) is attributed to volcanism-related extension. Lateral advection

of the block bounded by the MVFS and the Philippine fault zone (PFZ), rather than pure shear resulting from an assumed east–west

compression, best explains the observed kinematics of the MVFS. This is the result of compression during the westward drift of the

Philippine Sea Plate and northern Luzon and occurs through slip along the WMVF and EMVF at rates of 5–7 mm/yr.

D 2005 Elsevier B.V. All rights reserved.

Keywords: Fault segmentation; Slip rate; Neotectonics; Kinematics; Marikina

1. Introduction

The 135-km long dextral Marikina Valley fault sys-

tem (MVFS) or Valley fault system (PHIVOLCS, 1999)

is a major fault transecting the eastern portion of Metro-

politan Manila and belongs to a system of faults and

subduction zones that accommodates oblique conver-

0040-1951/$ - see front matter D 2005 Elsevier B.V. All rights reserved.

doi:10.1016/j.tecto.2005.11.009

* Corresponding author. Fax: +63 2 9207058.

E-mail addresses: [email protected] (R.E. Rimando),

[email protected] (P.L.K. Knuepfer).1 Tel.: +1 607 777 2389.

gence between the Philippine Sea Plate (PSP) and the

Eurasian Plate (Fig. 1). The over 1600 km-long Philip-

pine fault zone (PFZ) is an active sinistral structure that

extends from Luzon to Mindanao. The 1990 Luzon

earthquake was centered along one of its splays, the

Digdig fault. The PFZ accommodates much of the rela-

tive movement of the two plates between the trench

systems and may act to decouple the northwestward

movement of the PSP from the southeastward movement

of the Eurasian plate. An alternative view is that the PFZ

accommodates the boundary-parallel component of the

overall plate convergence as a trench-linked strike-slip

(2006) 17–38

Fig. 1. Tectonic setting of active faults in northern and central Luzon. The Marikina Valley fault system (MVFS) is bounded by major structures

including the Philippine fault zone (PFZ) on the east. Directly east of the east Luzon trough is a topographic high (Benham rise) within the

Philippine Sea Plate (PSP). Direction (3058 azimuth) and rate (8.0 cm/yr) of PSP motion after Seno et al. (1993). Numbers refer to the following

faults: 1 — Bangui; 2 — Bornay R.; 3 — Vigan–Vintar; 4 — Abra R.; 5 — Chico R.; 6 — Asin; 7 — Hapap; 8 — Eastern Cordillera; 9 — Coastal

Thrust; 10 — Casiguran; 11 — San Fernando; 12 — Mirador; 13 — Pugo; 14 — San Manuel; 15 — San Jose; 16 — Tebbo; 17 — East Zambales;

18 —Western Boundary; 19 — San Ildefonso; 20 — Lubang; 21 — Central Mindoro; 22 — Aglubang R.; and, 23 — Central Marinduque. Sources

of information for active faults: Rimando and Daligdig (1990), Nakata et al. (1977), Hirano et al. (1986), Punongbayan et al. (1991), Malterre

(1989), Geomatrix Consultants (1996), Intera (1995), Pinet and Stephan (1990), Rimando et al. (1995), and, Pinet (1990).

R.E. Rimando, P.L.K. Knuepfer / Tectonophysics 415 (2006) 17–3818

fault related to the Manila trench and/or the Philippine

trench (Fitch, 1972; Karig, 1983; Yeats et al., 1997). The

known and predicted slips of the PFZ and most of its

splays are consistent with this west-northwest to north-

west motion of the PSP. The Digdig fault and the PFZ are

predominantly sinistral strike-slip faults (although there

is a considerable reverse component across the Digdig

fault). Except for its northeastern portion, the predomi-

nantly dextral MVFS strikes parallel to the N–S-trending

portion of the Digdig fault and to the PFZ directly east of

the MVFS. Current GPS data cannot resolve MVFS’

kinematics given the large uncertainty involved, and

Thibault (1999) suggested that resolvable movement

across the MVFS is minor. Nevertheless, a dextral

sense of strike-slip is indicated by the longer-term,

near-field slip data presented in this paper. How slip is

accommodated among the faults is important to under-

standing the nature of the plate boundary; this paper will

in part address this issue.

The MVFS branches southward from the PFZ

(Fig. 2) and bounds the Marikina Valley, the northern

part of which is interpreted as a pull-apart basin. We

have not investigated the nature of the junction of the

MVFS and PFZ in detail due to logistical constraints.

The southern part of the East Marikina Valley fault

(EMVF) lies on the western side of the Southern Sierra

Madre, whereas the West Marikina Valley fault

(WMVF) bounds the west side of the valley (Fig. 2).

The MVFS appears to terminate to the south against

another tectonic feature, the Macolod Corridor (Fig. 2),

which is a zone of volcanoes related to northeast-

trending extensional structures that define a rift. The

rifting front is located south of Tagaytay Highlands.

However, the rifting front does not coincide with any

known faults, so its location is only approximate. The

trace of the WMVF farther south of the ridge, if it

exists, has been buried by young eruptive materials

from Taal Volcano.

Fig. 2. The main physiographic and tectonic elements in central Luzon related to the MVFS. The northern half of the MVFS cuts across the

Southern Sierra Madre while its southern parts bound the mountain range. The EMVF branches from the PFZ while both the EMVF and the WMVF

appear to terminate near the rifting front of the Macolod Corridor. The kinematics of the MVFS is attributed to the lateral extrusion of the block

between MVFS and the PFZ on the east. An complementary mechanism is clockwise rotation of the same block that is being extruded laterally.

Preliminary assessment of MVFS segmentation is also shown. Numbers refer to the structural/geometric segments shown in detail in Fig. 3.

R.E. Rimando, P.L.K. Knuepfer / Tectonophysics 415 (2006) 17–38 19


This study will contribute to understanding the style,

nature and distribution in space and time of some of the

deformation resulting from plate interactions in the

Philippines. Knowledge of these effects will also con-

tribute to the understanding of plate kinematics and

geometry of subducting plates and their boundaries.

Mapping of active fault traces and associated morpho-

logic features will contribute in evaluating the role the

MVFS plays in the plate boundary. In addition, more

reasonable assessments of the nature, timing and size of

future surface ruptures along the MVFS can be made,

which are of critical importance to estimating seismic

hazard and risk for Metro Manila.

2. Methodology

Lack of seismicity, historical events and fault plane

slickensides and lineations limited previous papers

from presenting convincing evidence on its kinematics,

Fig. 3. Strip maps of active traces of the MVFS. Associated morphotecton

delineation of MVFS’ active traces and, hence, in determining segmentation

detailed segment maps: a) Rodriguez–Taguig segment (I); b) Sucat–Binan se

(IV); e) San Mateo–Rodriguez segment (VI); f) Antipolo segment (VII

Interpretations were from 1:15,000 to 20,000 scale aerial photographs. Cir

each site are shown in Table 3.

although it has often been stated that it is a dextral

strike-slip fault (Gervasio, 1968; Arcilla, 1983; Arcilla

et al., 1989; Rimando et al., 1991; Punongbayan et al.,

1992). We document many geomorphic features along

and related to the MVFS through aerial-photo- and

field-based investigations to better understand the kine-

matics and recent activity of the MVFS. This study also

uses quantitative displacement data from offset geomor-

phic features as evidence for kinematics of the MVFS.

Among the most distinctive characteristics of active

strike-slip faults is an array of distinctive physiograph-

ic features (Sylvester, 1988). The San Andreas fault in

California was studied extensively following the 1906

San Francisco earthquake and so was the first place

where strike-slip movement was convincingly demon-

strated (Hill, 1981; Sylvester, 1988; Wallace, 1990).

Most workers in paleoseismology (Matsuda, 1975;

Slemmons, 1977, 1981; Wallace, 1977, 1978; McCal-

pin, 1996) relate the recency of faulting to the fresh-

ic landforms and displaced features along the fault were key to the

pattern of the fault system. These features are shown on the following

gment (II); c) Binan–Sto. Domingo segment (III); d) Pittland–Sungay

); g) Angono segment (VIII), and; h) Talim Island segment (X).

cled letter and number codes refer to measurement sites and data for

Fig. 3 (continued).


Table 1

Data for active faults in northern and central Luzon

Fault Length Extent Criteria Dominant type of faulting

Philippine fault zone

Digdig N125 km Dingalan Bay to Kayapa,

Nueva Vizcaya

Various geomorphic

features and offset streams

and landforms; seismicity

(16 July 1990 7.8 Ms);

historical accounts

Left-lateral strike-slip with

thrust component

Northern Digdig ~58 km Kayapa, Nueva Vizcaya to

Sabita, Benguet

Various geomorphic

features and offset streams

and landforms

Left-lateral strike-slip

Abra River ~220 km Near Sabita, Benguet to

Pasaleng Bay

Uncertain epicenter plots;

offset streams and

geomorphic features


Pugo (Kapangan) ~50 km Near Pugo–Rosario (La

Union) area, west of

Baguio, to La Union–Ilocos

Sur boundary

Shallow seismic events;

offset streams and

geomorphic expression


large thrust component

San Jose–San Manuel ~85 km Rizal, Nueva Ecija to

Lingayen Gulf

Historical accounts;

geomorphic features and

offset landforms and

streams


Tebbo ~45 km San Manuel, Pangasinan to

Itogon, Benguet

Historical accounts;


offset landforms and

streams


Hapap ~210 km Near Sta Fe, Nueva Vizcaya

to near Lallo, Cagayan;

northern segment follows

NE-trending reach of Chico R.

Geomorphic features;

diverted drainages


large thrust component

Other faults

Vigan–Vintar ~132 km SE of Vigan to Bacsil,

Ilocos Norte

Recent seismicity; offset

recent landforms

Thrust

Bornay River ~20 km SE from Dingras, Ilocos

Norte for about 20 km


recent landforms

Normal

Bangui ~200 km Bangui Bay to NW of

Ilagan, Isabela



Holocene deposits

Left-lateral strike-slip fault

Chico River ~40 km East–west from Pasil to east

of Tabuk, Kalinga–Apayao

Recent shallow

earthquakes; geomorphic

features

Marikina Valley fault

system

~130 km NNE direction from south

of Canlubang, Calamba,

Laguna towards the

Umiray–Dingalan Bay area

Offset geomorphic features

and streams

Right-lateral strike-slip

Casiguran fault ~200 km Generally follows the

coastline of Cagayan,

Isabela and Aurora

Historical accounts and

recorded seismicity;

geomorphic features

Thrust

East Zambales N125 km Extends from Sula, Tarlac to

Lingayen Gulf

Geomorphic features; recent

seismicity

Thrust?

Hundred Islands ~45 km Dasol, Pangasinan to NE

Hundred Islands

Uplifted marine terraces Thrust

Coastal thrust ~150 km Near Lingayen Gulf to near

Vigan, Ilocos Sur

Displacement of young

sediments as seen in seismic

profiles

Thrust

Western boundary

fault zone

~300 km West of Bataan to west of

Ilocos Sur

Geomorphic features;

uplifted marine terraces


Asin ~50 km Salcedo, Ilocos Sur to

Pidigan, Abra

Geomorphic features Thrust


Table 1 (continued)

Fault Length Extent Criteria Dominant type of faulting

Iba fault N50 km Vicinity of Angeles City to

Botolan, Zambales

Geomorphic features; recent

seismicity

Strike-slip?

Lubang fault N130 km West of Lubang Island

through Puerto Galera to

east of Verde Island

Recent seismicity and

historical accounts

Strike-slip

Sources: Rimando and Daligdig, 1990; Nakata et al., 1977; Hirano et al., 1986; Punongbayan et al., 1991; Malterre, 1989; Geomatrix Consultants,

1996; Intera, 1995; Pinet and Stephan, 1990; Pinet, 1990.


ness of appearance and type of geomorphic expres-

sion. Such landforms include the most recent scarps

along the MVFS; Rimando (2002) analyzes the rela-

tion between the degree of degradation of these scarps

and relative ages of events along the active fault

segments. Aerial photos taken in the 1950s and

1960s solve part of the problem posed by landform

erosion, and agricultural and infrastructure develop-

ment and have enabled us to produce neotectonic

strip maps for the MVFS (Fig. 3), which show a

variety of these fault-formed structures.

Vertical and horizontal displacements of offset or

deflected streams and channels, ridge crests, and allu-

vial fan axes or fan heads were measured directly from

aerial photographs. Calculation of height differences of

piercing points from 1:20,000-scale aerial photos using

parallax bar readings follows a similar method outlined

by van Zuidam (1986). Errors were not quantified for

offset data from field studies. Horizontal displacement

is measured directly using a transparent ruler. Although

lateral displacement measurement errors were not quan-

tified, uncertainty was minimized by making horizontal

and vertical measurements only where piercing points

are clearly correlatable across the fault. As an error

minimization measure, the mean of several differential

parallax measurements was quoted for each point.

3. Previous studies

Analysis of the recent movement of the MVFS

during the Holocene is germane both to understanding

the kinematics of the complex strike-slip fault plate

boundary and to evaluating seismic hazards of the

metropolitan area. The bgrabenQ nature of the Marikina

Valley was originally recognized by Alvir (1929) and

Irving (1947). Gervasio (1968) and Arcilla et al. (1989)

suggested earlier strike-slip faulting preceding a distinct

graben-forming period. None of these early studies

dealt with aspects of Holocene deformation along the

MVFS. The introduction to the Philippines of mapping

techniques employing tectonic geomorphology and

paleoseismology in the early 1990s has led to partial

mapping of features related to active faulting (Rimando

et al., 1991; Punongbayan et al., 1992). The results of

the GPS survey by Yu et al. (1999) between 1996 and

1998 and involving a few stations across the PFZ, the

MVFS and the east Zambales fault do not adequately

resolve relative motion between blocks across the struc-

tures in the area due to the large error relative to the

velocity difference between the station west of the east

Zambales fault and the station east of the MVFS. Other

papers (Rangin et al., 1999; Beavan et al., 2001;

Ohkura et al., 2001; Hamburger et al., 2003) have

also discussed the rotation of Luzon and of its known

blocks based on GPS data but these provide insufficient

information regarding the existence and senses of rota-

tion domains across structures in the MVFS region.

Thibault (1999) reports minor movement across the

MVFS, but attributes it to groundwater withdrawal in

the Metro Manila area. Detailed mapping for the pres-

ent study covers the WMVF and EMVF from the

Rodriguez, Rizal area to south of Canlubang, Calamba,

Laguna. Detailed mapping of the northernmost part of

the MVFS was done more recently in the Dingalan–

Umiray area (Aurora and Quezon Provinces) and in the

Binangonan–Antipolo areas.

Mainly because of the lack of neotectonic data on

faults in the region, including the MVFS, earlier stud-

ies that dealt mainly with the PFZ (Irving, 1951;

Allen, 1962; Barrier et al., 1991) are not adequate to

define the deformation mechanisms on a block-scale

to explain the recent kinematics of structures in the

region. We have compiled a list of active faults in the

region based mostly on an inventory done by

Rimando and Daligdig (1990), and Geomatrix Con-

sultants (1996) (Fig. 1; Table 1). Many of the faults

shown in Fig. 1 and Table 1 are thrust faults or strike-

slip faults with large thrust components. This compi-

lation of the active faults in northern and central

Luzon, coupled with the increased understanding of

the MVFS in this study, helps in resolving the defor-

mation mechanism and the role of the MVFS and

other structures in accommodating deformation in

the northern and central Luzon region.


4. Morphotectonic features along the MVFS

segments

Mapping of the MVFS reveals ten morphologically

distinct static segments or fault sections (Fig. 2). Al-

though the term fault section is preferred for static

segments (McCalpin, 1996), this study refers to these

simply as segments, which are herein distinguished

from earthquake or rupture segments. Large earth-

quakes sometimes rupture two or more static segments.

For hazard assessment purposes, this study’s main in-

terest is whether (and to what extent) individual static

segments along the MVFS link to form earthquake

segments. This is addressed in detail in Section 5 and

by Rimando’s (2002) modeling of fault-scarps.

Since there are no data available to directly define

actual rupture segments along the MVFS due to the

lack of seismicity, segmentation was initially assessed

mainly in terms of structural, geologic, and geometric

criteria previously defined by Knuepfer (1989) and

dePolo et al. (1989, 1991). Differences in the geomor-

phic character of the mountain fronts and presence of

bounding volcanic terrain were the main geologic cri-

Fig. 4. a) Examples of offset streams and triangular facets along segment I of

1966 aerial photos. b) Examples of offset streams and spurs, and other fault z

of the EMVF. These features were also recognized from the 1966 aerial pho

(Table 3).

teria applied. Branching of faults and intersections with

other faults were the structural criteria that were very

useful in differentiating many of the segments. Geo-

metric characteristics such as changes in fault orienta-

tion, stepovers, and gaps were also used to define the

segments.

Recognition of morphotectonic and offset features

both through the interpretation of aerial photos and

fieldwork provided the means for delineating active

traces and for obtaining evidence for their kinematics

(Fig. 3). A detailed strip map (Fig. 3a–h) has been

completed to show this evidence. Examples of the

evidence gathered from the interpretation of aerial

photos are shown in Fig. 4. Fault scarps are among

the most common features mapped from aerial photos.

We have profiled the most recent fault scarps (Fig. 5)

recognized in many locations in the field for relative

age determination (Rimando, 2002). The strip maps

provide the basis for identifying segments of the

MVFS, as described in Table 2 and more fully in the

following paragraphs.

Three of the segments shown in Fig. 3 and listed in

Table 2 are more than 20 km long (i.e., the ~45-km

the WMVF in the Rodriguez–San Mateo area and recognized from the

one geomorphic features along the Talim Island segment (segment X)

tos. Circled number and letter codes refer to offset measurement sites

Fig. 5. Examples of recent fault scarps along the MVFS. Most recent

fault scarps in Calamba, Laguna (a) along the Pittland–Sungay seg-

ment (segment IV). The recent fault scarps in Dingalan, Aurora (b)

and General Nakar, Quezon (c) are both along the Umiray segment

(segment V). These are among the numerous fault scarps identified in

the field that were instrumental in delineating the active traces of the

MVFS. Analysis of profiles of these scarps can provide relative ages

of events and aids in determining rupture segmentation (Rimando,

2002).


Rodriguez–Taguig segment or segment I, N37-km San

Mateo–Rodriguez segment or segment VI, and the ~35-

km Umiray segment or segment V), while the others are

15 km or less in length. Along the WMVF, the Rodri-

guez–Taguig (segment I), Sucat–Binan (II), Binan–Sto.

Domingo (III) and Pittland–Sungay (IV) are the more

significant segments. Except for segments I and II, the

precise location of the WMVF segments’ active traces

are mostly newly delineated in this study. The WMVF

may or may not terminate east of Mt. Sungay in the

Tagaytay Ridge. The southern terminus of the WMVF

is quite indistinct, probably due to very young volcanic

activity at Taal Volcano and the high rate of volcanic

sedimentation. Along the EMVF, only the San Mateo–

Rodriguez segment’s (segment VI) active trace had

been precisely delineated before this study. This is the

first time that evidence for recent activity and precise

location of active traces of the Talim Island (segment

X), Binangonan (segment IX), Angono (segment VIII),

Antipolo (segment VII), and Umiray (segment V) seg-

ments are mapped. This is also the first time that the

Talim Island and Binangonan segments are recognized

as active faults. Segments VII, VIII, IX, and X bound

the eastern part of the Marikina Valley and all have

similar orientation and kinematics with the other MVFS

segments. The northeast-trending Umiray segment(s)

extends from north of Rodriguez and dies out before

the coast in Umiray (south of Dingalan Bay) near the

northwest-oriented segment of the Philippine fault

(Figs. 1 and 2). This segment is less well-mapped due

to lack of aerial photographs and difficulties of field

access. Mainly based on its current creeping behavior,

the Sucat–Binan segment (II in Fig. 2) is herein con-

sidered a distinct segment. Details of tectonic control

and the role of groundwater withdrawal as a trigger for

the ongoing creep are discussed by Rimando and

Knuepfer (in preparation).

5. Quantitative data on kinematics of the MVFS

Inspection of the quantitative evidence consisting of

measurements of horizontal and vertical displacement

(Fig. 6a and b; Table 3) of offset features indicates that

the MVFS is dominantly a dextral strike-slip fault. The

displacement data can also offer insights into the rela-

tionship between the geometric segments mapped from

fault-trace analysis and the long-term persistence of

earthquake segments. Here, we examine the distinct-

ness of clusters of displacement values for the mapped

segments. If the vertical, horizontal, and net displace-

ments of segments of the MVFS are measures of the

length of their movement histories (or slip rate), then

lack of significant difference in the displacements indi-

cate that they have similar long-term histories. Signifi-

cant differences in the means of their V :H displacement

Table 2

Segments of the Marikina Valley fault system

Segment Name Criteria Length

WMVF

I Rodriguez–Taguig Geologic: geomorphic indicators such as range-front morphology (e.g., shutter

ridges, pressure and sidehill ridges, and scarps) and offset streams

~45 km

Structural: northern portion characterized by branching pattern

Geometric: northern segment of WMVF stepover; gap occupied by creeping

fault zone (segment II)

II Sucat–Binan Historic rupture limits ~14 km

Behavioural: segment characterized by creeping behavior of fault segments

arranged en echelon

Geologic: geomorphic indicators such as pre-existing tectonic scarps and scarps

formed by creep

Geometric: occupies gap area between segments I and III; creeping segments

arranged en-echelon; individual creeping segments oriented differently from

segments I and III

III Binan–Sto. Domingo Geologic: geomorphic indicators such as range-front morphology (dominated by

scarps) and offset streams

~12 km

Structural: southern end characterized by branching pattern

Geometric: southern segment of WMVF stepover; gap occupied by creeping fault

zone (segment II); separated from segment IV by stepover and gap

IV Pittland–Sungay Geologic: geomorphic indicators such as range-front morphology (dominated by

scarps) and offset/deflected streams

~7.5 km


Geometric: separated from segment III by a stepover and gap in faulting

Minor Northern boundary of

pull-apart basin

Behavioural: prehistoric rupture limits defined by multiple, well-dated

paleoearthquakes

~10 km

Structural: segment forms the northern boundary of a pull-apart basin

Geologic: geomorphic indicators such as range-front morphology (e.g., scarp), and

well defined linear depression/valley and offset streams

Geometric: segment defined by change in fault orientation

Minor Southern boundary of

pull-apart basin

Structural: segment forms the southern boundary of a pull-apart basin ~6.5 km

Geologic: geomorphic indicators such as range-front morphology

Geometric: segment defined by change in fault orientation

EMVF

V Umiray Geologic: geomorphic indicators such as range-front morphology (e.g., triangular

facets, scarps, saddles, pressure ridges) and offset streams

~35 km

Structural: branches from PFZ on the north

Geometric: defined by change in fault orientation; separated by gap from segment

on the southeast; stepovers

VI San Mateo–North

of Rodriguez

Geologic: geomorphic indicators such as range-front morphology (e.g., triangular

facets, saddles, shutter ridges, sidehill ridges, pressure ridges and scarps) and offset

streams and alluvial fans

~37 km


Geometric: northern end separated from segment IX by a gap

VII Antipolo Geologic: geomorphic indicators such as range-front morphology (e.g., triangular

facets, scarps, saddles and sidehill ridges), and narrow, linear valley.

~9 km

Structural: branches from segment V

Geometric: orientation changes from segment north of it

VIII Angono Geologic: geomorphic indicators such as range-front morphology (e.g., triangular

facets, scarps, saddles, pressure ridges, sidehill ridges and few shutter ridges),

large-scale narrow, linear valley and offset streams

~10 km

Geometric: segments defined by changes in fault orientation, stepovers, separations,

or gaps in faulting

IX Binangonan Geologic: geomorphic indicators such as range-front morphology (e.g., triangular

facets, scarps, saddles, pressure ridges, and sidehill ridges), narrow, linear valley and

offset streams

~13 km

Geometric: separation and step-over


Table 2 (continued)

Segment Name Criteria Length

X Talim Island Geologic: geomorphic indicators such as range-front morphology (e.g., triangular

facets, scarps, saddles, pressure ridges, sidehill ridges and shutter ridges) and offset

streams

~14.5 km

Geometric: segments defined by changes in fault orientation, stepovers, separations, or

gaps in faulting


ratios, however, suggest different styles of faulting. If

adjacent segments are similar, they probably have not

behaved independently over the long term; conversely,

significantly different displacements or displacement

patterns imply independent segment behavior. Our

analysis of the offset data in this section suggests

significant differences in displacement parameters.

Comparison of the segment displacements was accom-

plished by first drawing enveloping curves for the

displacement data in order to examine maximum dis-

placements along the fault. Even though many more

data points were measured (Table 3), the lack of age

control on offset geomorphic features precludes com-

paring all of the data; instead, we will assume that the

largest measured offsets are representative of a similar

period of Late Quaternary slip along the fault.

Table 4 summarizes the essential displacement pa-

rameter values. The difference in peak lateral and ver-

tical displacements is most pronounced for the segment

I-segment IV pair (Table 4; Fig. 6a). The greatest lateral

(155 m) and vertical displacement (~85 m) values along

the EMVF are both from the Talim Island segment

(segment X). The WMVF segments (Fig. 3) are char-

acterized by lower vertical displacement components

(Fig. 6a; Table 4) compared with those from the EMVF

segments (Fig. 6b; Table 4).

The differences in both the range and maximum

cumulative vertical displacement (Tables 3 and 4; Fig.

6b) between segments X and VI (San Mateo–Rodri-

guez) is most likely due to the influence of volcanism

which increases the tensional component across faults

(Van Wyk de Vries and Merle, 1998) near the southern

end of the fault zone (segment X) and does not neces-

sarily reflect differences in history or age of faulting.

For non-vertical fault-planes, dip-slip components

(Fig. 6c) are higher than the vertical components, but

trends for both components should be similar. The value

of fault plane dip is variable, but dip-slip component

was calculated assuming a 458 fault plane dip for all

measurement sites.

The net displacement (Fig. 6d) smoothes out along-

strike variations in lateral and vertical displacement.

Maximum cumulative net displacement differences

are significant only between segments I and IV (Fig.

6di) and between segments VI and X (Fig. 6dii). How-

ever, the difference between segments VI and X could

be attributed to the large vertical and horizontal com-

ponents of slip along segment X. For this reason, the

V :H ratio (Fig. 6e) is a preferred rupture parameter

(e.g., Lensen, 1958; Ramelli and Slemmons, 1990;

Berryman et al., 1992). In terms of the mean V :H

ratio, only those of segments X (0.88) and VI (0.35)

are significantly different from each other at the 0.05

level. However, differences between the maximum

V :H ratios of segments I (0.56) and IV (1.09), and

between those of segments III (0.69) and IV (1.09) are

significant. The difference between the maximum V :H

displacement ratios of segments VI (1.06) and X (1.46)

of the EMVF is less striking.

The mean V :H ratios for the whole WMVF and the

whole EMVF (at least for the portions covered by the

displacement data), are significantly different at both

the 0.01 and 0.05 significance levels. Clearly, this is

attributable to the large vertical component of slip along

the EMVF. This also implies a higher uplift rate and a

style of faulting that deviates slightly from the pure

dextral faulting of the WMVF. This also explains why

there is greater relief between the Marikina Valley and

the block on its east than the relief between the valley

and the block on its west.

We use the minimum and maximum single-event

scarp heights observed in the field for each segment

to estimate the range of the number of surface-rupture

events that may have generated the largest vertical off-

sets measured along each geometric/structural segment.

A total of 52 scarp profiles from the segments of the

MVFS was gathered. No recent scarps from three seg-

ments east and southeast of the Marikina Valley (seg-

ments X, VII and VIII) were found. As mentioned

above, differences in long-term movement histories

could reflect differences in rupture histories. The few

single-event lateral offset data gathered from the field

were also used along with the maximum horizontal

displacements measured from the aerial photographs

to obtain an independent set of similar estimates for

each segment. The number of surface-rupture events

derived from available scarp height, lateral and vertical

offset data are compared in Table 5. For the WMVF


segments, the estimates are based solely on the scarp

height and vertical offset data. The range for segment

VI of the EMVF (22–61) is near the upper limit of the

ranges for segments I, III and IV. Segment VI appar-

ently has a different frequency of movement than seg-

ments I, III and IV based on the vertical offset data. The

estimates on the number of events based on lateral

Fig. 6. Plot of displacement parameters versus distance for the MVFS. Plots

the WMVF and the EMVF, respectively. Dip-slip component plots (c) are

the WMVF (i) and the EMVF (ii) are also shown in d). The error bars

Though error bars are proportionately larger for smaller displacements t

displacement values would hardly change. Plots in e) are for the ratio of ve

indicate distribution of maximum offsets measured along fault. Roma

displacement data were collected.

displacement for segments VI and X are within the

lower end of the estimates for segments I, III, IV and

VI based on vertical offsets. As mentioned above,

however, these are based on a very limited number of

field measurements of lateral offset.

If the average recurrence interval obtained from the

Maislap trench site (adjacent to site M1 in Fig. 3a;

a) and b) are for the horizontal (i) and vertical (ii) displacements for

shown for the WMVF (i) and the EMVF (ii). Net displacements for

reflect only the uncertainty for vertical displacement measurements.

han for larger displacements, the ratio between vertical and lateral

rtical offset to horizontal offset for WMVF (i) and EMVF (ii). Curves

n numerals indicate location of geometric segments from where

Fig. 6 (continued).


recurrence interval 400–600 yr; Nelson et al., 2000) is

applicable to the entire WMVF, then it took 21–31 kyr

for the 29 m of vertical offset to accumulate in an

estimated 53 events. No data are available to constrain

recurrence intervals along the EMVF, nor have we been

able to obtain independent estimates of the ages of the

offset surfaces, so the age of recent faulting cannot be

estimated based on offset alone. However, the similarity

in the range of single-event scarp heights between

segment VI and the segments from the WMVF indicate

that the EMVF has a longer history of recent faulting

because of its higher maximum vertical displacement

(or that the youngest offsets aren’t representative of the

longer-term history).

6. Hazard implications

The geomorphic evidence presented in this paper

and paleoseismic data (Nelson et al., 2000; Rimando,

2002; Rimando and Knuepfer, in preparation), suggest

repeated rupturing along the MVFS throughout at

least the Late Holocene. Although the near-field

GPS data is vague about the sense and magnitude

of its motion, the lack of present-day seismicity indi-

cates a stick-slip mechanism and, hence, a high po-

tential for future seismic event. Based on empirical

relationships among surface displacement, rupture

length, and magnitude (Matsuda, 1975; Slemmons,

1977; Bonilla et al., 1984; Wells and Coppersmith,

1994), reasonable assumptions regarding maximum

magnitudes of future earthquakes along the MVFS

or its segments may be made. We first assume that

the individual segments defined above rupture inde-

pendently to estimate a probable minimum magnitude

of future earthquakes. The rupture segmentation in-

ferred from our analysis of the displacement para-

meters and most recent, single-event scarps

(Rimando, 2002), however, can be used to define

the more probable estimates.

Using a V :H ratio (0.16) obtained from aerial pho-

tograph measurements adjacent to and directly south-

west of the Maislap trench site (M-1 in Fig. 3a), and

assuming a persistent ratio of lateral to vertical dis-

placement, we came up with a probable earthquake

magnitude of M 6.8–7.1 for the offsets observed in

the trench (Nelson et al., 2000). We also use the max-

imum net displacements from the WMVF and EMVF

and from each segment derived from the maximum

Table 3

Horizontal, vertical, dip-slip, and net displacement data of recent offset features along the MVFS

Site Distance

from south

Lat.

disp.

St. dev. Vert. disp. Dip slip Net disp. Reference Remarks

Mean V Low V High V Mean Low High Mean Low High

West Marikina Valley fault (WMVF)

Rodriguez–Batasan (northern segment I)

RT1 74.9 20 0.0 20.0 20.0 20.0 Offset stream V IND but close to zero

RT2 74.1 100 0.0 100.0 100.0 100.0 Offset channel edge/stream V IND prob. due to adjustment of

stream to new base level

RT3 73.7 100 0.7100 5.6 4.9 6.3 7.9 6.9 8.9 100.3 100.2 100.4 Offset channel V estimated from topo map is 4–5 m

RT4 72.1 22.5 1.1600 12.6 11.4 13.7 17.8 16.1 19.4 28.7 27.7 29.7 Offset stream

RT5 71.4 67.5 1.2200 3.8 2.6 5.0 5.4 3.7 7.1 67.7 67.6 67.9 Offset stream and alluvial

fan (?) or mudslide (?)

RT6 73.5 20 0.7900 4.7 3.9 5.5 6.7 5.6 7.8 21.1 20.8 21.5 Offset stream

RT7 70.5 37.5 0.8500 3.8 2.9 4.6 5.3 4.1 6.5 37.9 37.7 38.1 Offset spur and channel

edge (for lat. disp. only)

RT8 70.2 30 1.0900 2.5 1.4 3.6 3.6 2.0 5.1 30.2 30.1 30.4 Offset channel

RT9 68.8 40 0.0 40.0 Offset terrace V IND but close to zero

RT10 68.3 80 0.0 80.0 Offset channel edge V IND

RT11 68.0 40 0.0 40.0 Offset terrace V IND but close to zero

RT12 69.0 29 2.0 2.8 29.1

Maislap (part of segment I)

M1 78.1 70 0.9500 11.3 10.3 12.2 15.9 14.6 17.3 71.8 71.5 72.1 H =offset stream/channel

V=Offset spur

V is max. because spur is sloping

and the fact that pts. of measurement

are not adjacent

M2 79.0 250 2.4700 29.0 26.5 31.4 41.0 37.5 44.5 253.3 252.8 253.9 Offset spur

M3 79.2 140 1.6900 21.8 20.1 23.4 30.8 28.4 33.2 143.3 142.8 143.9 Offset spur

M4 77.7 0 1.3700 9.5 8.2 10.9 13.5 11.5 15.4 13.5 11.5 15.4 Offset spur

Fort Bonifacio (southern segment I)

FB1 49.1 105 0.8400 3.6 2.8 4.5 5.1 3.9 6.3 105.1 105.1 105.2 Offset spur

FB2 48.4 44 0.0 44.0 44.0 44.0 Offset stream V IND but almost zero

FB3 47.4 15.8 0.7200 3.4 2.7 4.2 4.9 3.8 5.9 16.5 16.3 16.9 Offset spur

FB4 39.3 15 0.0 15.0 15.0 15.0 Offset channel ridge V IND but close to zero

FB5 39.1 30 0.9800 2.7 1.7 3.7 3.8 2.4 5.2 30.2 30.1 30.4

FB6 38.8 22.5 0.6500 1.6 1.0 2.3 2.3 1.4 3.2 22.6 22.5 22.7 Offset channel/stream

FB7 38.8 80 0.8200 2.4 1.6 3.3 3.5 2.3 4.6 80.1 80.0 80.1 Offset spur

FB8 36.8 75 1.9900 3.7 1.7 5.7 5.2 2.4 8.0 75.2 75.0 75.4 Offset spur

Carmona–Canlubang (segments III and IV)

L1 20.81 80 1.3500 5.6 4.3 7.0 8.0 6.1 9.9 80.4 80.2 80.6 Offset stream and channel edge

L2 20.0 60 0.7600 5.6 4.9 6.4 7.9 6.9 9.0 60.5 60.4 60.7 Alluvial fan (not cut—trace is

right at foot of mountain front)

displaced from source stream

R.E.Rimando,P.L.K.Knuepfer

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415(2006)17–38

30

L3 19.8 170 0.8600 9.4 8.6 10.3 13.3 12.1 14.5 170.5 170.4 170.6 Offset stream

L4 17.9 55 0.8900 7.1 6.2 8.0 10.0 8.8 11.3 55.9 55.7 56.1 Offset stream

L5 17.5 25 1.3000 4.6 3.3 5.9 6.5 4.7 8.3 25.8 25.4 26.4 Offset stream

L6 17.0 18 1.3300 3.8 2.5 5.1 5.4 3.5 7.3 18.8 18.3 19.4 Offset stream/alluvial fan

L7 16.7 25 0.8500 1.7 0.8 2.5 2.3 1.1 3.6 25.1 25.0 25.3 Alluvial fan (not cut—trace is



L8 16.6 20 Alluvial fan (not cut—trace is



L9 14.4 140 1.2400 6.8 5.6 8.1 9.6 7.9 11.4 140.3 140.2 140.5 Offset spur

L10 14.3 80 1.2900 4.4 3.1 5.7 6.2 4.4 8.1 80.2 80.1 80.4 Offset stream

L11 14.1 110 1.6300 21.1 19.5 22.7 29.8 27.5 32.1 114.0 113.4 114.6 Offset spur

L12 13.8 45 1.4300 4.5 3.0 5.9 6.3 4.3 8.3 45.4 45.2 45.8 Offset spur

L13 12.7 160 1.6100 16.4 14.8 18.1 23.3 21.0 25.5 161.7 161.4 162.0 Offset spur

L14 11.6 19 2.2100 13.1 10.9 15.4 18.6 15.5 21.7 26.6 24.5 28.9 Offset spur

L15 6.4 35 0.8700 3.1 2.2 3.9 4.3 3.1 5.5 35.3 35.1 35.4 Offset stream

L16 6.3 24 1.8900 26.1 24.2 28.0 36.9 34.3 39.6 44.1 41.8 46.3 Offset/deflected stream




East Marikina Valley fault (EMVF)

North Montalban–San Mateo (segment VI)

R1 75.1 42.5 1.2200 14.0 12.7 15.2 19.7 18.0 21.5 46.9 46.2 47.6 Offset stream

R2 74.9 55 4.6800 9.4 4.7 14.1 13.3 6.7 19.9 56.6 55.4 58.5 Offset stream

R3 74.8 35 1.2500 5.2 3.9 6.4 7.3 5.6 9.1 35.8 35.4 36.2 Offset stream

R4 74.7 25 3.3900 6.0 2.6 9.4 8.4 3.6 13.2 26.4 25.3 28.3 Offset stream

R5 72.7 32 0.8300 17.6 16.8 18.4 24.9 23.7 26.1 40.5 39.8 41.3 Offset spur

R6 72.6 25 0.9700 15.2 14.2 16.2 21.5 20.1 22.9 33.0 32.1 33.9 Offset spur

R7 72.5 25 1.4200 6.5 5.1 7.9 9.2 7.2 11.2 26.6 26.0 27.4 Offset channel

R8 71.8 40 3.1500 42.4 39.2 45.5 59.9 55.5 64.4 72.1 68.4 75.8 Offset spur

R9 68.1 120 0.8500 11.6 10.8 12.5 16.4 15.2 17.6 121.1 121.0 121.3 Offset stream

R10 68.0 37.5 1.3100 4.8 3.4 6.1 6.7 4.9 8.6 38.1 37.8 38.5 Offset stream

R11 67.3 35 1.0600 3.6 2.6 4.7 5.1 3.6 6.6 35.4 35.2 35.6 Offset ridge (not spur)

R12 70.0 4.8 4.0 5.6 7.4

R13 75.5 8.3 1.1 1.5 8.4

R14 69.5 4.5 1.0 1.4 4.7

Talim Island (segment X)

T1 31.0 67.5 2.8100 83.8 80.9 86.6 118.5 114.5 122.4 136.3 132.9 139.8 Offset spur

T2 24.7 155 1.8400 55.3 53.5 57.1 78.2 75.6 80.8 173.6 172.5 174.8 Offset spur

T3 25.1 150 1.8300 65.6 63.8 67.5 92.8 90.2 95.4 176.4 175.0 177.8 Offset stream/valley axis (Derived height minimum due to

sedimentation on downthrown side

and erosion on upthrown valley)

T4 23.5 37.5 1.9500 54.9 52.9 56.8 77.6 74.9 80.4 86.2 83.7 88.7 Offset spur

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Table 4

Summary of displacement parameter values

Segment Length (km) Maxiumum H (m) Maximum V (m) Max. dip-slip (m) Max. net displ. (m) V :H ratio

Average Maximum

Segment I 45 250 29 41 255 0.26 0.56

Segment II 14 – – – – – –

Segment III 12 170 21 30 171 0.26 0.69

Segment IV 7.5 100 26 37 102 0.12 1.09

Segment V 35 85 – – – –

Segment VI 37 120 42.5 60 122 0.40 1.06

Segment VII 9 – – – – – –

Segment VIII 10 – – – – – –

Segment IX 13 – – – – – –

Segment X 14.5 155 84 119 180 0.40 1.46

WMVF 87.5 250 29 41 255 0.24 1.09

EMVF 115 155 84 119 180 0.46 1.46


single-event scarp heights and V :H ratios (and by

assuming a 458 fault plane) for estimating magnitude.

Wells and Coppersmith’s (1994) regression between

moment magnitude and maximum displacement for

strike slip faults was used. The magnitudes obtained

from maximum displacement range from 7.4 to 7.7 and

are consistently higher than magnitude estimates using

segment length (Table 6).

Estimates based on this method should be treated

with caution. For example, our active fault trace map-

ping suggests a branching pattern in the Maislap area

indicating that rupturing may not be confined along a

single trace. Thus, Nelson et al. (2000) may have under-

estimated the probable magnitude at the Maislap trench

Table 5

Estimates of the number of earthquake events from offset data

Segment Maximum Maximum Range of single-e

V (m) H (m) scarp height (m)

WMVF

Segment I 29 250 0.55

3.4

Segment III 21 170 0.65

1.4

Segment IV 26 100 0.5

1.8

EMVF

Segment V – 85 0.3

3.4

Segment VI 42.5 120 0.7

1.9

Segment VII – – –

Segment VIII – – –

Segment IX – – 0.2

1.2

Segment X 84 155 –

–

exposure, as displacement could have been distributed

across multiple fault strands. Although the use of max-

imum net displacement minimizes uncertainty due to

along-fault variation in horizontal and vertical displace-

ment, our estimates assume that the V :H displacement

ratio is uniform along a fault segment. The displace-

ment data near Maislap and along other segments sug-

gest otherwise (Table 3; Fig. 6a–e), but we do not have

sufficient data to be able to improve on this assumption.

In addition, assuming a 458 dip of the fault plane tends

to narrow the range of the magnitude estimates. The

estimates shown in Table 6 also suffer from uncertain-

ties inherent to the Wells and Coppersmith’s (1994)

regressions.

vent Range of single-event Est. no. of events based on

hor. displ. (m)V H

– 53 –

– 9 –

– 32 –

– 15 –

– 52 –

– 14 –

5.5 – 15

6.3 – 13

4.5 61 27

7.1 22 17

– – –

– – –

2.2 – –

3.3 – –

– – –

– – –

Table 6

Magnitude estimates based on length of segments and maximum displacement

Segment Length Max. scarp height

(single-event)

Dip-slip V :H ratio

(average)

Max. net displ. Est. mag. based

on length

Est. mag. based

on offset

Segment I 45 3.42 4.84 0.26 14.0 7.0 7.7

Segment II 14 – – – – 6.4 –

Segment III 12 2.25 3.18 0.26 9.3 6.4 7.6

Segment IV 7.5 1.77 2.50 0.12 15.0 6.1 7.7

Segment V 35 3.38 4.78 – – 6.9 –

Segment VI 37 1.9 2.69 0.40 5.5 6.9 7.4

Segment VII 9 – – – – 6.2 –

Segment VIII 10 – – – – 6.3 –

Segment IX 13 1.22 1.73 – – 6.4 –

Segment X 14.5 – – 0.40 – 6.5 –

WMVF 87.5 3.42 4.84 0.24 15.3 7.3 7.7

EMVF 115 3.38 4.78 0.46 8.8 7.5 7.5


The magnitudes for the WMVF, the EMVF and the

shorter geometric/structural segments were also esti-

mated based on Wells and Coppersmith’s (1994) re-

gression between moment magnitude and surface

rupture length (Table 6). Except for segment I, the

estimated magnitudes for the shorter geometeric/struc-

tural segments are less than M 7, as their lengths are

less than 45 km. As mentioned earlier, however, a

structural/geometric segment is not necessarily equiva-

lent to an earthquake rupture segment. This study does

not exclude the possibility of larger magnitude earth-

quakes rupturing the whole length of the WMVF or the

EMVF.

This possibility is reinforced by the similarity be-

tween the length-based magnitude estimates for both

the WMVF and the EMVF on the one hand, and the

offset-based magnitude estimates for the WMVF and

the EMVF on the other. If a maximum offset along a

particular geometric segment was produced by a rup-

ture that involved that segment independently, we

would expect similar magnitude estimates for length

and offset. Instead, the magnitude estimates for indi-

vidual segments using length and offset are substantial-

ly different (Table 6). In particular, the lower length-

based estimates imply that the offsets are too large for

single-segment ruptures. In contrast, the estimates from

offset and length (7.3 from length and 7.7 from offset

for the WMVF, 7.5 from each calculation for the

EMVF) are consistent when the faults are considered

as a whole. This suggests multi-segment rupturing

along the EMVF and the WMVF. Considering the

uncertainties involved in the estimation of magnitude

based on offset and surface rupture length, this study’s

estimates indicate that the MVFS has had a history of

generating earthquakes greater than M 7 along the

WMVF and the EMVF.

Finally, we use the empirical relationship between

magnitude, recurrence and slip rate formulated by

Slemmons and dePolo (1986) as modified from Mat-

suda (1975) and Slemmons (1977) to estimate slip rate

based on magnitude and recurrence inferred from the

Maislap trench site (400–600 yr; Nelson et al., 2000).

For segment I, the offset-based M 7.7 is equivalent to a

slip rate of 7–10 mm/yr while the rupture length-based

M 7 corresponds to 1.5–3.5 mm/yr. Assuming that the

estimate for segment I is applicable to the entire

WMVF then the offset-based slip rate is 7–10 mm/yr

while the slip rate based on its rupture length (87.5 km)

is 6–8 mm/yr. For the EMVF, the rupture length- and

offset-based magnitudes are the same and correspond to

a slip rate of ~6–8 mm/yr. These estimates are consis-

tent with the cumulative displacement-based slip rate of

8–12 mm/yr (based on the 1 :8.5 V :H Maislap site

ratio) for segment I or 5–7 mm/yr (based on 1 :4 V :H

ratio) for the entire WMVF.

7. Tectonic framework of structures in Northern

Philippines and kinematic role of the MVFS

Understanding the more significant aspects of the

region’s tectonics is also critical in resolving the role

of the MVFS in plate boundary deformation. The east

Luzon trough has been interpreted as a subduction

zone either in its incipient stage (Fitch, 1972), or as

a reactivated convergent margin (Hamburger et al.,

1983; Lewis and Hayes, 1983). However, seismic

evidence (Hamburger et al., 1983; Bautista, 1996)

indicates the lack of a well-defined Wadati–Benioff

zone across the east Luzon trough and active under-

thrusting or interplate displacement along the Manila

trench. Kreemer et al. (2000) indicate only a small

amount of convergence across the east Luzon trough.


This reinforces the possibility that east Luzon trough

only partially accommodates motion of the Philippine

Sea Plate and that the northern Luzon landmass along

with the rest of the Philippine Sea Plate is being

pushed westward essentially as a whole over the

Eurasian plate. Additional evidence includes the arcu-

ate shapes of the archipelago and the PFZ in the

northern Philippines, the configuration of the Manila

trench suggesting migration in the direction of motion

of the faster overriding plate (Wu, 1978), and apparent

westward drift of the east Luzon trough from the

Philippine trench. The Benham rise (Fig. 1) east of

the trough is probably a factor in resisting or retarding

subduction of the Philippine Sea Plate along the east

Luzon trough (Ben-Avraham and Nur, 1987; Bautista,

1996). A slowdown in subduction could be accommo-

dated by deformation west of the east Luzon trough

and/or along the Manila trench. The resulting plate

shortening may be manifested by mountain building

and thrusting along active faults. Thrust faults that

dominate the eastern portion of northern Luzon and

a system of active strike-slip faults (including the PFZ

and its splays), some of which have large thrust

components (Table 1; Nakata et al., 1977; Pinet and

Stephan, 1988; Malterre, 1989), accommodate part of

the deformation in northern Luzon (Fig. 1; Table 1).

What then is the role of the MVFS in this tectonic

environment? The dextral strike-slip MVFS is orient-

ed and behaves like a conjugate with the sinistral

strike-slip PFZ in the area of their intersection at

the north end of the MVFS. However, the N–S-ori-

ented southern portion of the MVFS is almost parallel

to both the northern portion of the Digdig fault and

the PFZ to the east of the MVFS. Dextral strike-slip

faulting along the MVFS is not kinematically congru-

ent with the assumed E–W-oriented compression in

the region (Punongbayan et al., 1982; Arcilla, 1983).

It appears that the block bounded by the PFZ and

MVFS is being extruded laterally. This mechanism

closely resembles advection of crustal blocks through

indent-linked strike-slip faults (Woodcock, 1986;

Yeats et al., 1997). Examples of indent-linked strike-

slip faults include those that have resulted from the

collision between India and Tibet–southern China

(Molnar and Tapponnier, 1975, 1978; Avouac and

Tapponnier, 1993) and those in central Japan resulting

from the convergence between the Pacific and Eur-

asian plates (Sugimura and Matsuda, 1965). England

and Molnar (1990) departed from models that empha-

size thrusting and extrusion of crustal blocks between

strike-slip faults and upheld the more significant role

of lithospheric thickening in the deformation of Asia.

The discrimination between the competing dkinematic

modelsT, which emphasize localized deformation

through major strike-slip faults bounding quasi-rigid

blocks (e.g., Molnar and Tapponnier, 1975, 1978;

Tapponnier et al., 1982; Avouac and Tapponnier,

1993; Peltzer and Saucier, 1996; Tapponnier et al.,

2001), and ddynamic modelsT, which favor distributed

accommodation of deformation (e.g., Vilotte et al.,

1982; England and Molnar, 1990, 1997; Houseman

and England, 1993; Molnar and Gipson, 1996; Holt et

al., 2000; Zhang et al., 2004), rests on an increasing

amount of new geophysical and geological data and

geodetic measurements of slip and uplift rates (Tap-

ponnier, 1999).

The potential that block rotation is a significant

mechanism in the MVFS–PFZ region and controls the

kinematics and recent activity of the MVFS also must

be considered. Rotation of blocks and/or their bounding

strike-slip faults has been demonstrated during defor-

mation and shown to be widespread in many parts of

the world (Ron et al., 1984; Garfunkel and Ron, 1985;

Nur and Ron, 1987). Such rotations occur in many

different tectonic settings involving significant strike

slip faulting. Since the late 1990s, several papers

(e.g., Rangin et al., 1999; Yu et al., 1999; Beavan et

al., 2001; Ohkura et al., 2001; Hamburger et al., 2003)

have discussed the active kinematics of Luzon based on

GPS data. The GPS data indicate an anticlockwise

rotation of Luzon with respect to the Philippine Sea

plate. The relative motion of blocks across some major

structures in Luzon is also evident from the data but the

GPS sites are not sufficiently widely distributed nor in a

dense enough network to recognize more local displa-

cements and rotations in the MVFS region. The data of

Yu et al. (1999) from key sites are not significantly

different enough from each other to determine relative

motion of blocks across the MVFS. Ohkura et al.

(2001) focused on the kinematics of the region south

of the MVFS, where they demonstrated rotation on a

more local scale and suggested sinistral motion with

large amount of counterclockwise motion across the

Macolod Corridor with respect to the station northwest

of the Marikina Valley. Hamburger et al. (2003) also

recognized sinistral shear along the Macolod Corridor.

McCabe et al. (1987) present paleomagnetic data from

either side of the MVFS in the Manila area. While they

do not consider motion across the MVFS nor internal

block rotation, their Plio-Pleistoene data show a minor

counterclockwise rotation of the east side of the MVFS

with respect to the west side.

Block rotation seems a plausible mechanism in the

region, but data pertaining to the occurrence, timing,


extent of domains (and nature of reference boundaries),

senses, and magnitudes of rotation must be obtained

through further GPS, paleomagnetic, neotectonic, and

structural studies. Nevertheless, the results of our neo-

tectonic mapping can provide constraints to the senses

of rotation in the MVFS region and of the block

bounded by the MVFS and the PFZ. Extension and

sinistral slip across the Macolod Corridor would coun-

teract, in part, the tectonic escape that would seem to be

indicated by dextral slip on the MVFS and sinistral slip

on the PFZ, producing a clockwise rotation in response.

The known rates of slip of the PFZ (e.g., 15 mm/yr;

Geomatrix Consultants, 1996) are higher than the slip

rates of the MVFS that have been computed in this

study. Clockwise rotation of the region between the

PFZ and the NS-oriented portion of the MVFS is one

way of accommodating the differential slip.

Block rotation in conjunction with lateral extrusion

of the block between the PFZ and MVFS could explain

why the Macolod Corridor, a northeast-oriented zone of

northwest extension, is situated in a region that, due to

southward motion of the block bounded by the PFZ and

MVFS, is expected to be compressional. Extensional

zones such as those found on the trailing edge of the

Caribbean plate in northern Central America are be-

lieved to be tectonic responses to rotation (Burkhert and

Self, 1985). Alternatively, extensional zones are known

to be associated near the ends of and oblique to strike-

slip faults in regions of convergence (Molnar and Tap-

ponnier, 1975).

8. Summary and conclusions

Displacement data and morphotectonic features con-

sistently indicate a dominantly dextral strike-slip mo-

tion along the MVFS during the recent geologic past.

Larger-scale evidence for the present-day sense of

movement of the MVFS is that it forms a pull-apart

basin bounded on the east by the EMVF, and on the

west by the WMVF. The vertical component of dis-

placement is particularly large along the eastern fault

boundary of the pull-apart basin. A greater vertical

component also occurs on Talim Island (segment X)

where regional volcanism may be a factor in modifying

the stress regime. Recognition of neotectonic features

resulted in the precise mapping of active traces and

static segments of the MVFS that were previously

unrecognized.

Understanding of the geometry and recent kinemat-

ics of the MVFS allows better appreciation of the

longer-term history of its movement. Large vertical

displacements are not necessarily the result of a distinct

phase of the MVFS’ development, despite the sugges-

tions of some previous workers (Alvir, 1929; Irving,

1947; Gervasio, 1968; Arcilla et al., 1989). Instead, the

vertical component of slip during the contemporary

phase of deformation that has generated strike-slip

faulting may account for all of the vertical deformation.

Significant differences in V :H ratios of the WMVF

and EMVF indicate slightly dissimilar styles of fault-

ing, with the WMVF having a dominantly dextral

movement and the EMVF oblique dextral. The larger

cumulative slip of the EMVF and the similarity in the

range of single-event scarp heights from the WMVF

and EMVF segments could indicate differences in the

age of faulting, slip rate, and/or recurrence interval. Our

analysis of the displacement data further suggests that

rupturing along the EMVF has involved multiple seg-

ments and has most likely occurred separately from the

events along the WMVF segments. The occurrence of

earthquakes along segments I and IV at different times

is also suggested. However, our results do not preclude

contemporaneous rupturing of the WMVF and the

EMVF. As suggested above, variation in the style of

faulting along the MVFS may be the localized result of

transtension or volcanism. The offset-based magnitude

estimates for the WMVF and EMVF fall within the

range M 7.3–7.7. Similarity in magnitude estimates

from offsets and from total fault length for the

WMVF and EMVF supports multi-segment ruptures.

Considering only the offset data and results of the static

segment mapping, the MVFS has the potential of gen-

erating M N7 earthquakes.

The kinematic role of the MVFS is strongly con-

trolled by the recent tectonic evolution of Luzon. Sub-

duction along the east Luzon trough is retarded due to

the presence of the Benham rise east of the trough.

Compression during the en masse drift of northern and

central Luzon towards the west along with the rest of

the Philippine Sea Plate resulted in the development of

structures such as thrust faults and strike-slip faults with

large thrust components in the northern Philippines.

Deformation is also accommodated through subduction

along the Manila trench and through mountain building

in northern Philippines. To accommodate compression

the block bounded by the sinistral PFZ and the dextral

MVFS is extruded laterally through advection.

The motion of this block may also involve rotation.

In other strike-slip fault areas, rotation accounts for the

development of extensional regions similar to the

Macolod corridor at the south end of the MVFS. Future

work should verify the possible contributions of the

kinematics and dynamics of tectonic features in the

region to block rotation. Further structural and neotec-


tonic mapping and a more comprehensive GPS survey

involving more stations in strategic sites should help

resolve the pattern and rate of tectonic motions in the

region.

The WMVF and the EMVF move at similar rates

during the extrusion process. Based on recurrence of

400–600 yr inferred from a previous paleoseismic in-

vestigation (Nelson et al., 2000), the amount of cumu-

lative displacement and the length of segments, the

average slip rate for the WMVF is about 5–7 mm/yr.

Maximum slip rates of 7–10 mm/yr and 6–8 mm/yr

were estimated for the WMVF and the EMVF, respec-

tively, based on the empirical relationship between

magnitude, recurrence and slip rate formulated by

Slemmons and dePolo (1986) as modified from Mat-

suda (1975) and Slemmons (1977). Magnitudes used in

the estimation, however, are considered maximum. The

Digdig fault of the Philippine fault zone, on the other

hand, accommodates deformation in the region at a

faster rate of ~15 mm/yr (Geomatrix Consultants,

1996). The complexities imposed by plate dynamics,

and plate and fault boundaries explain why, in many

instances, the orientations and kinematics of structures

may no longer be interpreted by simply applying the

classic Andersonian principle of brittle failure.

Acknowledgments

For the constructive comments, we thank Professors

Francis T. Wu and William D. MacDonald of the

Department of Geological Sciences and Environmental

Studies, SUNY at Binghamton, and Prof. J. Ramon

Arrowsmith of Arizona State University for comments

on an earlier draft of this paper. We gratefully acknowl-

edge PHIVOLCS (Philippine Institute of Volcanology

and Seismology) for logistical support for the study. We

also thank Alan Nelson (U.S.G.S.) and Takashi Nakata

(Hiroshima University) for useful discussions. Com-

ments by Manuel Pubellier and Mike Sandiford im-

proved the manuscript considerably.

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