1. 用近震波形分析2013 年6 月2 日南投地震的震源過程 謝銘哲1, 趙里2, 馬國鳳1 1國立中央大學地球物理研究所
2 中央研究院地球科學研究所

2. Outline Real-time Focal Mechanism Determination
Generalized Cut and Paste method (gCAP) in 1D structure
Revised Focal Mechanism in 3D Structure
Improve focal mechanism solution in 3D structure
Real-time Finite-fault Determination
Determine average rupture property
Resolve fault-plane ambiguity

3. Point Source Focal Mechanism Determination in 1D Structure
CWB Earthquake
Early Warning
System (EEWS)
EEWS Report
(Eq. long/lat)
Focal Mechanism Determination
System Triggered
BATS Waveform
Records Cut
SAC Files Prepared
Rotation to
R/T components
Waveform Traces
Selected
Grid Search for
Best Solution
Generate Output
and Exit
Iteration
gCAP
gCAP: generalized Cut And Paste
(Zhu & Ben-Zion, 2013)

4. 1D Point Source Solution of 02 June 2013 Nantou Earthquake
Real-time gCAP solution failed for this event due to the saturation of records at SSLB station (Δ≈10.3km).

5. 3D Green’s Function Database
Source grids
to 60-km depth
(2.4km spacing)
2282 Receiver grids
on the surface
(4 km spacing)
Model: Kuo-Chen et al. (2012) + ETOPO1
Green’s functions calculated by finite-difference (Zhang and Chen, 2006).

6. Broadband Record and 3D Synthetics (≤ 0.8Hz)
YULB-HHE
h=5km
h=10km
h=15km
h=20km
sec
Broadband 3D synthetics calculated using gCAP mechanism agree with records very well. Visual comparison suggests a source depth of km?

7. Upper-Band Record and 3D Synthetics (0.05Hz-0.3Hz)
YULB-HHE
h=5km
h=10km
h=15km
h=20km
sec
Source depth km?

8. Lower-Band Record and 3D Synthetics (0.02Hz-0.1Hz)
YULB-HHE
h=5km
h=10km
h=15km
h=20km
sec
Source depth 5-10 km?

9. Broadband Record and 3D Synthetics (≤ 0.8Hz)
TWGB-HHZ
h=5km
h=10km
h=15km
h=20km
sec
Ratio of surface and P wave amplitudes is also diagnostic of source depth (10 km?).

10. Upper-Band Record and 3D Synthetics (0.05Hz-0.3Hz)
TWGB-HHZ
h=5km
h=10km
h=15km
h=20km
sec
Source depth 5-10 km?

11. Lower-Band Record and 3D Synthetics (0.02Hz-0.1Hz)
TWGB-HHZ
h=5km
h=10km
h=15km
h=20km
sec
Source depth km?

12. Revising Focal Mechanism in 3D Structure
Depth 20k m, Mw 6.04
Plane-A: S/D/R= 12°/24°/90°
Plane-B: S/D/R=192°/66°/90°
gCAP
Teleseismic
Regional
Mw 6.2
Depth 25km
Mw 5.73
Depth 23km
Mw 6.0
Depth 16km
gCAP result as initial model
Grid search parameters in 3D model
Depth: 10 – 30 km
Strike: 337° - 47°, dip: 4° - 44°, rake: 55° - 125°
each at an interval of 5°
Grid search of 18,225 point sources
Waveforms fitting are measured by L2-norm errors and an iterative scheme
Moment magnitude (Mw) is solved by balancing amplitudes of available stations
6 stations (20 3-comp. P and surface wave traces)
0.02Hz-0.1Hz for surface wave
0.05Hz-0.3Hz for P-wave (first arrival)

13. Focal Mechanism in 3D Structure gCAP Point Source in 3D Teleseismic
Depth 12.0 km, Mw 6.05
Plane-A: S/D/R= 342°/29°/55°
Plane-B: S/D/R=201°/67°/108°
Teleseismic
Regional
Mw 6.2
Depth 25km
Mw 5.73
Depth 23km
Mw 6.0
Depth 16km

14. Simplified Models for Finite-Source Rupture Scenario Search
Possible Rupture Speeds
Possible Types
55% β
75% β
95% β
Circular (6)
(2 planes)
Unilateral (48)
(2 planes)
3 possible rupture speeds for each direction
Bilateral (72)
(2 planes)
9 possible rupture speeds for each direction
Fault plane dimension is estimated by scaling-law study (Yen and Ma, 2011)

15. Average Rupture Model for 0602 Event
75% β
AU420
The best average finite-fault model shows a rupture on the east-dipping plane propagating unilaterally from NE to SW with an upward component at 75% of shear-wave speed.
STR/DIP/RAK
342°/29°/55° SW NE
RMS errors of 126 finite-fault models

16. Average Rupture Model for 0327 Event
95% β
75% β
AB323
The best average finite-fault model shows a rupture on the east-dipping plane propagating horizontally with 95% of shear-wave speed to SW and 75% of shear-wave speed to NE.
STR/DIP/RAK
42°/22°/114° SW NE
RMS errors of 126 finite-fault models

17. Comparisons with Aftershock Distribution - 0327 and 0602 events -
From CWB

18. Comparisons with Shake Intensity
Point Source Synthetic PGV
Finite-Fault Synthetic PGV
CWB Intensity Observation

19. Conclusion
Overall comparisons of synthetics and records show that the 3D model of Kuo-Chen et al. (2012) predicts good P waveforms up to 3-sec period.
Relative amplitudes between surface and P waves suggest that 0602 Nantou earthquake has a centroid depth of ~10 km.
The 0602 Nantou earthquake is a unilateral rupture on the east-dipping fault plane propagating NE-to-SW with an upward component at 75% shear-wave speed. The 0327 and Nantou earthquakes have similar rupture scenarios.

20. Finite-Fault Simulation
Finite-fault waveform simulation
(2-sec Gaussian STF, ~ 0.8 Hz )
- 3-D velocity model
ETOPO1 topography
Finite-Fault Simulation
Z-component

21. Thanks for your attention.