Building up Seismsic Models for Ground Motion
Prediction of Taiwan: Problems and Challenges

Kuo-Fong Ma
馬國鳳
Institute of Geophysics
National Central University

What approaches we can make toward areliable PSHA map• How reliable is reliable? Definition? Can we provide thedefinition? to public? to government?
Approaches
1. Identifying the seismic source models
2. Estimation of the recurrence intervals of each source
model
3. Ground Motion Prediction Equation (GMPE): Give aneasy and quick reference number in PGA and PGVempirically, but, large variance in values (stress drops?)
Finite-Fault Simulation: give a full waveforms from 010Hz (maybe), but, time consuming and many
assumptions in fault model (fault geometry, asperities). A
requirement of a fine 3D velocity structure for modelingof high frequency.

Seismic Source Models (Shyu et al., 2005)

Active Fault Mapping（Shyu et al., 2005）

How to characterize the earthquake
scenario of the seismic source models• Fault Segment, geometry, mechanism
GMPE => PGA and PGV (now in PSHA, but,large variance in values)• Slip distribution (Sa) on the fault=> near-fault
PGD, PGV, and PGA (GMPE, and full-waveform
simulations), and far-field long period wave andthe duration of shaking. (Shall we consider thisin PSHA?)
If yes, how can we do it? => study of historicalearthquakes.

Steps: PSHA=>Deterministic PSHA (Japan)

Damaging Earthquakes in Taiwan since 1700s
M>7 inland
earthquake~ every 100years

Relative quiet in seismicity

WesternTaiwan~every30-40years

Three M>7earthquakes
in twomonths

How to characterize the earthquake
scenario of the seismic source models• Slip distribution (Sa) on the fault=> near-fault
PGD, PGV, and PGA (GMPE, and full-waveform
simulations), and far-field long period wave andthe duration of shaking. (Shall we consider thisin PSHA?)
If yes, how can we do it? => study of historicalearthquakes• Offshore large events (un-expecting eventsin Ryukyu and Manila Trenches, analog toTohoku earthquakes?), other un-expecting
inland large event?

Bathymetry and Tectonic Setting surrounding Taiwan

Outra-ordinary Earthquake
Potential around Taiwan:-1909 style moderate depthhigh stress drop intra-plate events

Taiwan-1920 M8.0 earthquake, but, rupture
all the way to the trench as Tohoku
earthquake-Possible rupture pattern along theManila trench (1781 tsunamis?)
How to incorporate these into PSHA?

PGA attenuation curve
Yang, and Ma (2012)
InterDepth=
15 km

IntraEvent5-Sparse in data
-Better fit to Japanese curve- within variance for inter-plate event

JapanTaiwan

Depth=
65km

Event11-Values beyond the GMPE-- Still better fit to Japanese curve-- EGF provides good estimationJapan1909 Taipei Earthquake(Kanamori, Lee and Ma, GJI, 2012)

M6.5-7.0
Depth~ 80km

1909 Taipei earthquake recorded at Hongo

Seismicity with focal depth < 30 km

ML

Seismicity concentrates
at the lower‐edge of the fault

Epicenterof 331 EQ~M8 EQ

GaguaRidge~M8 EQ122.5ºE

123ºE

1990‐2010
Yaru Hsu (personal communication)
124ºE

Plausible
rupture zone

Seismicity concentrates
at the lower‐edge of the fault

Distance from trench (km)Seismicity is absent to theeast of the Gagua ridge

Scaling using AREA
and STRESS DROPh : seimogenic depthβ: scaling parameter related
to the effective fault width- Small-Moderate earthquakes
Mw ~ LogA- Large earthquakes
Mw ~ 4/3logA- Extra largest earthquakes
Mw ~ 2/3logAA)
22HM  log A  log
 const .
A3[1  max(1, 2 )] / 2
H max(1,(Shaw, 2009)

Const.: Stress drop related constantTaiwanCalifornia

Predict Ground Motion of a large event from smaller event
Simulation from EGF (high and regular stress drop events)
NO.

Date(UTC)

Latigude(deg)Longitude(deg)depth(km)MLMwstrikediprakeM1 (16) 1999/10/22 03:10

120.43123.533

16.74

6.00

5.90

45.00

90.00

170.00m1a1

1999/10/23 21:53

120.433

23.540

14.83

4.46

4.05

346.76

56.41

16.18

M2 (6)

1998/07/17 04:51

120.660

23.500

2.80

6.20

5.88

45.00

50.00

110.00m2a1

2004/01/23 07:51

120.648

23.458

13.06

4.34

3.73

51.97

30.37

104.56

Results of assessed SMGA,
Simulated ground motions
and spectra

608.60 bars (10.00 km2)
643.00 bars ( 9.64 km2) Yen&Ma, 2011

Problems and Challenges (I)
PSHA (I), using GMPE from seismic source model (logic trees)
How to reduce the variance of GMPE
What’s the variance the Engineers can bear?
PSHA (I.1), GMPE- Considering AREA, STRESS DROP for inland events- GMPE for INTER- INTRA- (Collaboration with JAPAN)- Historical Earthquakes
Scenario Earthquake of Historical Earthquakes, 1906 Meishan Earthquake
Full waveform simulations, 0-10Hz- Construction of a fine reliable 3D velocity structure- Mapping shallow structure (seismic layer, engineering layer)- hybrid (EGF+3D, Stochastic + 3D)- Simulation of long-period wave (Duration)=> PSHA (II) Deterministic PSHA

Problems and Challenges (II)•How to incorporate the extreme event (as the events not yet
occurred in history), and less seismicity events (e.g. 1909 Taipei,1867 Keelung earthquakes) into PSHA,•Sharing Japan’s experience on the thoughts and questions
stated above.
•Can GEM provide the global guideline to the questions above?
e.g.
- How to reduce the variance in GMPE
- What to give in PSHA for public and government(no miss-leading)- Steps toward Deterministic model.

THANK YOU!

Ground Motion Prediction from EGF

m1
1996/07/29 Global CMTLon: 122.35 ；Lat:24.49
Depth:63km
Mw5.34ML6.14
m1a1
2001/12/16 BATS
Lon: 122.38 ；Lat:24.52
Depth:53km
Mw4.28ML5.1

Black:observations
Red: synthetics

Development of 3D wave propagation
modeling: 3D Ground Motion Simulation
For Taipei Basin in different Models
Basement +SunShang Formation

Only Basement

Layered Half-Space

By 李憲忠 Lee et al. (2009)

Active Fault Mapping（by 徐澔德, Shyu et al., 2005）

Ryukyu Trench
Seismicity (1997‐2003)

1920 M8.0 Earthquake(Wu et al., 2009)