26 july 2013 símon Ólafsson , eerc
DESCRIPTION
Scientific aspects of South Iceland earthquakes. 26 July 2013 Símon Ólafsson , EERC. Outline. Introduction Icelandic Strong Motion Network Estimation of source parameters Ground motion prediction equation (GMPE) Discrete time realization Conclusions. Historical earthquakes in the SISZ. - PowerPoint PPT PresentationTRANSCRIPT
26 July 2013Símon Ólafsson, EERC
Scientific aspects of South Iceland earthquakes
Outline
• Introduction• Icelandic Strong Motion Network• Estimation of source parameters• Ground motion prediction equation (GMPE)• Discrete time realization• Conclusions
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013
Historical earthquakes in the SISZ
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013
Icelandic Strong Motion Network
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013
Árborg Town Hall: The strong-motion array
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013
The Árborg Town Hall: Earthquake 29 May 2008, UTM 15:45
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013
Internet Site for the European Strong motion Database (ISESD)
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013
Recent earthquakes in South Iceland
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013
• Mw 6.0, 25 May 1987
• Mw 6.5, 17 June 2000
• Mw 6.5, 21 June 2000
• Mw 6.3, 28th May 2008
Ground motion model (Stochastic method)
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013
p 0 20 c c3
c 2c
12
C M R(M , , R , , , ) ( , ) ( , ) ( , ) ( )
21( , ) =
1+ ( / )1( , )
( , ) exp
( )
A B G E S
B Omega squared source model
G Geometrical spreading function
E Spectral attenuation
S Site amplification
R R
R R
Selection of S-wave window
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013
0 10 20 30 40 50 60 70 80-5
0
5x 10
-4 Longditudinal acceleration
0 10 20 30 40 50 60 70 80-2
0
2x 10
-4 Vertical acceleration
AC
CEL
ER
ATI
ON
(g)
0 10 20 30 40 50 60 70 80-5
0
5x 10
-4 Transverse acceleration
TIME (s)
Estimation of parameters
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013
M0 seismic momentDs stress drop = R/Q ‘spectral attenuation’
Moment magnitude Mw (Hanks-Kanamori): M Mw ( / ) log .2 3 10 70
Earthquake 28 May 2008 - Parameters
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013
Parameter Estimate Units _____________________________________Mo 3.4 ×1018 N mMw 6.26 Fc 0.24 Hzr 6.4 km 0.053 sDs 73.0×104 Pau 79.4 cm_____________________________________
Attenuation of PGA South Iceland June 2000
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013
0 10 20 30 40 50 60 70 80 90 1000
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
DISTANCE (km )
PG
A (
g)
Geometric spreading function
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013
12
n nD DD
R 1 2
2 3
D D DD D D
2 2 D d h
d = epicentral distanceh = depth parameterD1, D2 and D3 are used to set the limits for the
different zones of the spreading function
Derivation of GMPE
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013
dT2
rmsd 0
1a a(t) dtT
2
rmsd
A( )1a d2 T
Parseval theorem:
PGA (amax) related to rms-acceleration (arms) with peak factor (p): amax = parms
Theoretical GMPE
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013
2/32/3
10 10 10 10 10(2 7) 1 1log ( ) log log log ( ) log ( )
2 32 Ds
Prms o
d
C Ra M R
T
1 11 ci cos 3sin si sin 3cos
2 2
Attenuation for 29 May 2008
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013
Duration estimation
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013
0 20 40 60 80 1000
5
10
15
20
25
30
DISTANCE (km)
DU
RA
TIO
N (s
)
0 20 40 60 80 1000
5
10
15
20
25
DISTANCE (km)D
UR
ATI
ON
(s)
50%55%
60%65%
70%75%
80%85%90%
a) Duration based on 90% cumulative energy. The dotted red curve represent mean value +/- one standard deviation (+/-1s). b) The curves represent the duration function of Eqn. 3.10 for different fractions of total cumulative energy (50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% and 90%).
Ground motion simulation
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013
Discrete time realizations
Sub-filter
Time domain discrete representation
Brune H1
Savage H1
H2
H3
H4
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013
2 21 1 1( ) 2e ( 1) e ( 2) ( )x k x k x k w k
1 1( ) e ( 1) ( )a ax k x k w k
1 1 1 1 1 1 1 2
1 1 1 1 1 2
( ) ( 1) ( ) ( )( ) ( )
a a
a a
x k x k A x k M B x k M BA x k M B x k M B
2 1 1 12S
1( ) ( ( ) 2 ( 1) ( 2))x k x k x k x kT
2 1
3 22 21 S
( ) ( )2 / 2
pN n
n
zx k x k nnT
4 4 3( ) ( ) (1 ) ( )x k rx k n r x k m
Time domain equations for sub-filters representing discrete model.
Conclusions
• For the South Iceland earthquakes the near-field attenuation has a high rate of attenuation (R-2)
• Ground motion model (GMPE) has to include a geometrical attenuation term to accound for the fast rate of attenuation in the near-field
• GMPE based on a physical model can be applied to obtain ground motion parameters and for time series simulation
• For realistic simulation of ground motion time sequences a realistic estimate of duration is important.
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013
Introduction
• Examine relationship: Modified Mercally Intensity (IMM) vs. g
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013
Estimating parameters
• PGA, PGV: Use for example larger og two horizontal component, average of peak values for horizontal
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013
Intensities map
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013
0 10 20 30 40 50 60 70 80-5
0
5x 10
-4 Longditudinal acceleration
0 10 20 30 40 50 60 70 80-2
0
2x 10
-4 Vertical acceleration
AC
CEL
ER
ATI
ON
(g)
0 10 20 30 40 50 60 70 80-5
0
5x 10
-4 Transverse acceleration
TIME (s)