safer: seismic early warning for europe safer test - site report: bucharest by gh.marmureanu,...

SAFER: Seismic eArly warning For EuRope

SAFER Test - Site Report: Bucharest

by

Gh.Marmureanu, C.Ionescu, A.Marmureanu, C.O.Cioflan, B.Grecu, A.Danet

POTSDAM, GERMANY , June 3-5, 2009

The Tectonic of the Carpathian Arch - Vrancea Area


Bucharest is one of the cities most affected by earthquakes in Europe. Situated at 150-170 km distance from Vrancea epicenter zone, Bucharest had suffered many damages due to high energy Vrancea intermediate-depth earthquakes. For example, the March 4, 1977 event (Mw =7.2) produced the collapse of 36 buildings with 8-12 levels,while more than 150 old buildings were seriously damaged. The ruptured area was at 140 km on Nov. 10,1940 Vrancea earthquake( Mw =7.7), 110 km on March 4,1977(Mw =7.4), 134 km on August 30,1986(Mw =7.1) and 85 km on May 30,1990(Mw =6.9) depth.

The depth interval between 110 km and 130 km remains not ruptured since 1802, October 26, when it was the strongest earthquake occurred in this part of Central Europe.

The magnitude is assumed to be Mw =7.9-8.0 and this depth interval is a natural candidate for the next strong Vrancea event.




Geological section through Quaternary layers from Vrancea to Danube river



Isobaths are generally oriented from east to west, with a slope of about 8‰ dipping from south to north.


● Bucharest site amplifications by using very hard rock(VHR) and joint source site determination(JSSD) methods.

(i)- methods that calculate the site response with respect to a reference site located on a hard rock(VHR) and,

(ii)- methods that calculate the site response with respect to a reference site(JSSD), so called non-reference techniques.

We used as reference site a site located in Bucharest (INCERC) for which the geotechnical characteristics are known from the borehole existing in that place (thickness of the layers, velocity of the P and S waves, density).

The procedure for obtaining the local amplification functions was the following :(a)-selection of the S-wave windows of 10s length with good signal-to-noise ratio; (b)-computing the amplitude Fourier spectra for the horizontal components of the

selected windows;(c)-modeling the amplitude Fourier spectra for the “Very Hard Rock” site;(d)-computing the ratio between the amplitude Fourier spectra of the horizontal

components of earthquakes and the modeled amplitude Fourier spectra; (e)-computing the average ratio for each station.




Distribution of the K2

stations in Bucharest

area ( 42 K2 units)



Station BMG (VHR Method) Station BTM (VHR Method)

Station CIO (VHR Method) Station CNC (VHR Method)



Station INC(INCERC Bucharest)-only VHR Station BMG :JSSD & VHR MethodsThe amplification functions got by VHR and JSSD methods for K2 stations from Bucharest (The average- black color ;± 1 σ – red color)


Result 1:From the VHR and JSSD analysis:for the stations situated

downtown Bucharest (BGM, BST, BTM, BVC) the amplification functions show a decreasing tendency from small to high frequency.

At stations BGM and BTM a well defined peak can be observed between 3 and 5 Hz. This reaches 2.6 units of amplitude at station BGM and respectively, 3.8 units at BTM.

Station BAP indicates a high level of amplification (> 4 units) which is about constant for the considered frequency domain.

This characteristic can be also found at the K2 stations located in the vicinity of Bucharest city (CIO, CNC, MOG, POP, STF) except for the station BMG where an increasing level of amplification is noticed at intermediate frequencies with a maximum of 3.3 units at 5.2 Hz;



●Nonlinear Bucharest site amplifications by using spectral amplification factors (SAF) method.

(SAF)a= Samax /amax ; (SAF)v = Sv

max /vmax ; (SAF)d = Sdmax /dmax

amax =ÿ(t)max ; vmax =x˙(t)max and dmax = x(t)max


0 1 2 3perioada T [s]

0

100

200

300

400

SA

5%

com

p N

S

0 1 2 3 4 5 6 7P eriod [s ]

0

100

200

300

400

500

600

700

SA 5

%da

mpi

ng [g

/10]

IN C com p N SVR77VR86VR901

Vrancea-epicenter Bucharest-site



26.04 26.06 26.08 26.1 26.12 26.14 26.16

44.36

44.38

44.4

44.42

44.44

44.46

44.48

44.5

44.52

44.54

1.81.922.12.22.32.42.52.62.72.82.933.13.23.33.43.53.63.73.83.9

INC1

MET1MTR1

MLT1PND1

TIT1

BUC

OTP1

26.04 26.06 26.08 26.1 26.12 26.14 26.16

44.36

44.38

44.4

44.42

44.44

44.46

44.48

44.5

44.52

44.54

3.73.753.83.853.93.9544.054.14.154.24.254.34.354.44.454.54.554.64.654.74.754.84.85

INC1

MET1MTR1

MLT1PND1

TIT1

BUC

OTP1

Non - filtered 0.005-1.0 Hz


0.05 - 2 Hz 0.05 - 5 Hz Space distribution/dispersion of the SAF values in Bucharest area from Vrancea

earthquake on August 30,1986 (Mw =7.2)


26.04 26.06 26.08 26.1 26.12 26.14 26.16

44.36

44.38

44.4

44.42

44.44

44.46

44.48

44.5

44.52

44.54

3.05

3.1

3.15

3.2

3.25

3.3

3.35

3.4

3.45

3.5

3.55

3.6

3.65

3.7

3.75

3.8

3.85

3.9

INC1

MET1MTR1

MLT1PND1

TIT1

BUC

OTP1

26.04 26.06 26.08 26.1 26.12 26.14 26.16

44.36

44.38

44.4

44.42

44.44

44.46

44.48

44.5

44.52

44.54

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3

3.1

3.2

3.3

3.4

3.5

3.6

3.7

3.8

3.9

4

4.1

4.2

INC1

MET1MTR1

MLT1PND1

TIT1

BUC

OTP1


Result 2:There is a strong nonlinear dependence of the spectral

amplification factors of earthquake magnitude and site conditions (Marmureanu et al,2005).

Dispersion of the SAF values for strong motion records in Bucharest (Mw>6) shows a certain stability of SAF values for each frequency domain discussed (0.005 - 1Hz: 3.5- 4.6; 0.005-2Hz: 2.8 - 3.8 ) which can be used in rapid estimation of the seismic response on the city area (Figure 5).

The innovation is the nonlinear of SAF of magnitude



●Bucharest site amplification by using down-hole seismic measurements:Case A: Acceleration response spectra by using as input the

accelerogrames recorded at -100m depth to the surface during of Vrancea earthquake on October 27, 2004, Mw =6.00) –Bucharest City

Mean weighted seismic velocities for the seven main types of Quaternary layersGeologic layer Depth of the Density Mean weighted Vp Mean weighted Vs upper limit (m) (g/cm3) seismic velocity (m/s) seismic velocity (m/S) 1. Backfill 0.00 1.10 370 1672.Upper clay layer 0.50-5.00 1.75 687 2443.Colentina aquifer 5.00-12.00 1.99 1044 274 (sand+ gravel)4.Intermediate layer 10.00-20.00 2.07 1488 3275.Mostistea aquifer 15.00-35.00 2.00 1563 3406.Lacustrine layer 35.00-50.00 2.14 1753 3977.Fratesti aquifer 100.00-185.0 2.05 1740 545 (sand +gravel)


The depths of the boreholes : Basilescu:-172m; Foradex :-81m; Grivita:-110m; Iorga:-170m; Policolor:-100m;Buciumeni:-150m;Otopeni:-200m;Politehnica:-200m; IMGB: -155m; Magurele:-112m;Centura 1:-80m and Centura 2:-60m.


Case B:The amplification of the seismic signals in Bucharest by using as input at -52m the signal recorded at - 52m deep,at City Hall Bucharest,during on Oct. 27.2004 Vrancea earthquake (Mw =6.00)

Mean weighted Vs, Vs-30 and Vs-50 seismic velocities in the first Quaternary layers Layer 1 Layer 2 Layer 3 Layer 4 Layer 5 Layer 6 Vs-30 Vs-50

1.Tineret Park 140 220 299 - 398 - 263 3402.Ecology Univ. 120 220 241 354 390 401 286 3263.Astronomy Inst. 120 260 330 350 390 433 283 3204.Titan 2 Park 160 250 250 350 381 450 299 3415.Metrodrom Park 200 200 320 393 410 410 288 3276.Student Park 210 210 342 270 375 400 295 319 7.Basilescu Park 160 160 317 390 408 - 294 3348.Rom. Shooting Fed. 210 330 350 400 400 - 327 3479.Geological Museum 180 310 322 - 376 - 320 32810.NIEP site 250 350 320 337 410 410 326 338Mean weighted Vs (m/s) 169 252 320 367 386 417




Peak Acceleration (g)

PRI EW/ 27.10.2004

PRI NS/ 27.10.2004

Average

De

pth

(m

)

Ecologic Univ. 12 layers - Earthquake 27.10.2004

-10

-20

-30

-40

-50

00.00 0.02 0.04 0.06 0.08 0.10

The variation of the peak acceleration from - 52 m depth to the surface at site Ecology Univ. for the two input horizontal ground motions: PRI_EW(PGA=0.022g) and PRI_NS (PGA=0.013g) recorded at - 52 m in borehole during of Vrancea earthquake on October 27,2004 (Mw =6.0)●Case C: The amplifications of PGA during of Vrancea earthquake on Oct. 27, 2004(MW =6.00) in other 6 boreholes made in Bucharest City. The Vrancea earth-quake on Oct.27,2004(Mw=6.00) was recorded in 6 boreholes in depths between free field level and -153m

SAFER: Seismic eArly warning For EuRopeStation Deep sensor Shallow sensor Surface sensor (free filed) Depth PGA(g) Depth PGA(g) PGA(g) The amplification (1) (2) (3) 3: 1 3 : 21.UTCB NS 0.0165 0.0285 0.0349 2.115 1.225 EW -78 m 0.0231 -28 m 0.0146 0.0584 2.528 4.000 V 0.0098 0.0111 0.0344 3.510 3.0992.UTCB NS 0.0156 0.0216 0.0416 2.667 1.926 EW -66 m 0.0235 -28 m 0.0168 0.0409 1.740 2.435 V 0.0070 0.0115 0.0248 3.543 2.1573.NCSRR/ NS 0.0113 0.0139 0.0297 2.628 2.137 INCERC EW -153m 0.0114 -24 m 0.0125 0.0296 2.596 2.365 V 0.0067 0.0083 0.0249 3.716 3.0004.Civil Prot. NS 0.0127 0.0203 0.0290 2.283 1.283 Hdq. EW -68 m 0.0194 -28 m 0.0131 0.0492 2.536 3.756 V 0.0088 0.0112 0.0340 3.864 3.036 5.City Hall NS 0.0132 0.0166 0.0298 2.258 1.795 EW -52 m 0.0222 -28 m 0.0377 0.0790 3.559 2.095 V 0.0096 0.0118 0.0331 3.448 2.8056.Municipal NS 0.0126 0.0116 0.0546 2.459 4.707 Hospital EW -70 m 0.0181 -30 m 0.0185 0.0445 2.459 2.405 V 0.0089 0.0082 0.0508 5.708 6.195



Result 3. The variation of the peak acceleration from - 52 m depth to the surface at site Ecology Univ. for the two input horizontal ground motions (PGA= 0.022g) recorded at -52 m in borehole during of Vrancea earthquake on Oct.27, 2004(Mw=6.0) is between 0.06 g and 0.10 g . This is consistent with the maximum values recorded in Bucharest for the earthquake on 27.Oct. 2004 whose borehole recordings were used as input. We didn’t use amplification factors similar to those of Borcherdt;

Result 4: The scattering of the amplifications between PGA recorded by deep ,shallow and surface/free field K2 sensors in Bucharest site was made obvious by measurements made in 6 boreholes with real data for last Vrancea earthquake on Oct.2004(MW =6.0). The ratio between surface sensors and deep ones is between 2.115 and 5.708. The average is 3.912.

The innovation: for the first time we can see the nonlinear quantitative amplification between sensors placed at: -153 m, -78 m, -70 m, -68 m, -66 m and -52 m and surface sensors;



●Frequency dependent PGA/PGV amplification analysis

●


Observed distribution of macroseismic intensity during the large Vrancea earthquakes (November 10,1940, Mw = 7.7 and March 4,1977, Mw = 7.4).



Distribution of maximum accelerations for last significant Vrancea earthquake on Oct.27,2004(Mw=6.0;h=98 km).(Grecu et al)


The earthquakes affects very large area with a predominant NE-SW orientation (“banana” shape),characteristic response spectra with large periods of 1.5-1.6 seconds, no significant attenuations on Romanian territory, large amplifications away etc.


Functions of amplification dependent on region (Sokolov,Grecu etc.)



The observed macroseismic map and the modeled distribution of ground motion parameters (MSK intensity,PGA ,PGV) for the major Vrancea earthquake on March 4,1977(Mw =7.4 ; h= 95 km).


Result 5:The maps outline the following features: the general orientation of the isoaccelerations on the NE-SW direction, small value of accelerations in epicenter areas (0.1626 g) and areas with large values of accelerations situated far from the epicenter (0.314 g at 32 km ,in Focsani , August 30,1986,Mw =7.2) (Grecu,2008);

Result 6: The average values of amplification can vary signifi-cantly from one region to another depending on the frequency range. The region “South-West” (Bucharest) the highest amplifications are in the range of 0.6 to 4 Hz (Grecu et al, 2004). The region “South” shows almost the same amplification for frequencies greater than 1.0 Hz. The increase of amplification toward low frequencies ( region “South-West”) may be explained by the influence of the surface waves generated within the deep sediments of the Moesian platform.


SAFER: Seismic eArly warning For EuRope●Attenuation laws to Bucharest by using different models (Joyner-Boore, Crouse etc.)PGA in epicenter area (Vrancioaia) during of August 30,1986 Vrancea

earthquake(Mw =7.0) was 0.1626 cm/s2 , in the north of Bucharest was 0.156 cm/s2 while in the south-est of it was only 0.0763 cm/s2 .

Ln(amax) = c1 + c2 MGR + c3 ln R +c4 h + σ ln amax .P Ln(amax)= 4.726 + 0.976 MGR -1.146 ln R - 0.0066 h + 0.353 P Earthquake MGR Depth (h,km) ∆ (km) R (km) amax (recorded) amax (computed)

1.March 4,1977 7.2 110 100.37 148.91 198.00 cm/s2 199.00 cm/s2

2.August 30,1986 7.0 143 123.25 188.78 95.30 cm/s2 95.55 cm/s2

3.May 30,1990 6.7 90 173.53 195.48 98.70 cm/s2 102.05 cm/s2


Result 7: Each parameter for each zone(i) is obtained from “reference station” INCERC Bucharest:

Izonei = (I)INCERC ± Δ I (MMI scale);(amax )zonei = (amax )INCERC ± Δ a in (cm/s2)

(T,s )zonei =( T,s )INCERC ± Δ T,s in seconds ,i=1...14The base is the seismic hazard map( microzoning ) of Bucharest



The innovation:Reference

station„concept”:

Izonei = (I)INCERC ±

Δ I (MMI scale);

(amax )zonei = (amax) INCERC ± Δ a in

(cm/s2)

(T,s )zonei =( T,s)INCERC ± ΔT,s in seconds i=1…14 zones


●Attenuation laws and intensity map by using the azimuths and the concept of “etalon earthquake” to get so-called “banana” shape

It was observed that all epicenters are on the same line NE-SV (direction AB) and also for maxim macroseimic intensity I0 -direction A’B’ which is parallel to epicenter line AB at distance D0 of 23 km.


Epicentres E(line AB) and I0 (line A’B’) points corresponding to the four strong and major earthquakes (MGR 6.7) occurred in the last 69 years

SAFER: Seismic eArly warning For EuRopeThe earthquake on August 30,1986 is used by us “control

earthquake concept ” in all studies as it fulfils the following states:(i)-it was strong (Mw =7.2); (i)-it was recorded in a lot of seismic stations on Romanian territory;

(iii)-the fall plan solutions are very closed (almost identically) to

other Vrancea stronger earthquakes(Nov. 10, 1940; Mw =7.7 and March 4,1977;Mw =7.4) and with majority of earthquakes with moderate magnitudes (6.9 < Mw <7.2);

(iv)-the depth of oh hypocenter (h≈131-143 km) is very close to medium value of all strong Vrancea earthquakes.

Log I(X,Az)=Log I0X+Log (Ie /Ioe )Az +b(Az)Log[Re /f ( he )/RX / f(x) ]Az +[c log δ ]Az

where:IOX is the maximum intensity of an earthquake at a depth h=x ; δ is the directivity factor of the rupture propagation in the focus ; c is the way how the directivity factor may influence the directivity of the seismic source ; Re = (Δ2 +he2 )1/2 ; RX =(Δ2 +x2 )1/2 ; Δ is the distance between the observation point of maximum macroseismic intensity.



Result 8:By using the earthquake

on Aug. 30,1986 as “control earthquake” it was obtained the “banana” shape of the attenuations curves family of the macroseismic intensity I (along the directions defined by azimuth Az), in the case of an Vrancea earthquake at a depth 80< x ≤ 160 km.

The innovation part is the concept of “ control earthquake”.


The isoseismal map of the maximum possible Vrancea earthquake(MGR =7.5)


●Rapid magnitude determination for Vrancea early warning system.

NIEP early warning system consists of several different parts:

(i)-A dedicated acquisition system, algorithms to rapidly detect seismic events,

(ii)-Algorithms that eliminate false detections and alarms and methods to estimate the earthquake magnitude and to send the warning to the users. All of these parts have to work automatically, in real time, without interruption for a long period of time. As a fit between maximum 1Hz low-pass filtered vertical acceleration and Mw magnitude, the following relation was assumed ( Marmureanu A.,2009):

y=A1 e-x/t1 +y0

where A1=3.97902e-7 ; t1=-0.4029, y0=-9.69317e-4.

This can be used to approximate very well earthquake magnitude in the first seconds after detection . The average absolute error is 0.271 magnitude degrees using all existing recorded data. This error is satisfactory, taking into account that the magnitude is computed on 4-5 seconds after P wave is detected in the epicenter area .




Fit between maximum 1Hz LP filtered acceleration and Mw magnitude



Absolute error in magnitude estimation (|M computed – MROMPLUS|) for all recorded events at the three stations (MLR, VRI, PLOR)

Result 9 / Novelty: The software developed by NIEP was tested at last Vrancea earthquake on April 25, 2009 when the magnitude (Mw =5.7) of the earthquake was computed in first 5 seconds and it was an accurate value.


●Integrated of early warning system, alert, shake and disaster in disaster reduction and risk management

Early warning system is viewed as part of an real-time information system that provide rapid information, about an earthquake impeding hazard, to the public and disaster relief organizations before (early warning) and after a strong earthquake (shake map).

The USGS shake map software has been installed and modified for the Bucharest area.Two main problems have been encountered: first, the USGS software uses for site characterization VS-30 and second, the attenuation relationships implemented in the software are not valid for Vrancea earthquakes.

By using USGS shake map software, we can see shake map for strong Vrancea earthquake on Nov.10,1940 (Mw =7.7) and March 4,1977(Mw=7.4) which differ totally from observed distribution of macroseismic intensity.

Then, NIEP made the decision to use real data in real time. POTSDAM, GERMANY , June 3-5, 2009



Observed distribution of macroseismic intensity(left) and shake map made by using USGS “Shake Map” software for strong Vrancea earthquake on Nov.10,1940(Mw =7.7)



Observed distribution of macroseismic intensity(left) and shake map made by using USGS “Shake Map” software for strong Vrancea earthquake on March 4,1977 (Mw =7.4)



The epicenter and the alert map The place of EWS, alert, shake and disaster maps in seismic risk management


Result 10 / Innovation:The innovation with comparable or related systems worldwide is that NIEP

will use the EWS to generate a virtual shake map (alert map for Bucharest-140 km away of epicentre) immediately after the magnitude is estimated (in 4-5 seconds after the detection in epicentre) and later make corrections to construct real shake map by using real time dataflow from each K2 accelerometers installed in Bucharest area (42 K2 units), inclusively nonlinear effects, to generate shake map, in real time.

Thus, developing of a near real-time shake map for Bucharest urban area is of highest interest, providing valuable information to the civil defense, decision makers and general public on the area where the ground motion is most severe.




Thank you for your attention !

safer: seismic early warning for europe safer test - site report: bucharest by gh.marmureanu,...

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