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

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

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)

1D Point Source Solution of 02 June 2013 Nantou Earthquake http://tecdc.earth.sinica.edu.tw/FM Real-time gCAP solution failed for this event due to the saturation of records at SSLB station (Δ≈10.3km).

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).

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 10-15 km?

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

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?

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?).

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?

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

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)

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

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)

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

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

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

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

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 0602 Nantou earthquakes have similar rupture scenarios.

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 2013.06.02

Thanks for your attention.