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用近震波形分析 2013 年 6 月 2 日南投地震的震源過程

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

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用近震波形分析 2013 年 6 月 2 日南投地震的震源過程

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

  4. 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).

  5. 3D Green’s Function Database Source grids to 60-km depth (2.4km spacing) 2282Receiver 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 10-15 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 10-15 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 10-15 km?

  12. gCAP 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 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) Regional Mw 6.2 Depth 25km Mw 5.73 Depth 23km Mw 6.0 Depth 16km Teleseismic

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

  14. Simplified Models for Finite-Source Rupture Scenario Search • Possible Rupture Speeds • Possible Types • 55% β • Circular (6) • (2 planes) • 75% β • 95% β • 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 AU420 SW NE STR/DIP/RAK 342°/29°/55° • 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. RMS errors of 126 finite-fault models 75% β

  16. Average Rupture Model for 0327 Event AB323 SW NE STR/DIP/RAK 42°/22°/114° • 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. RMS errors of 126 finite-fault models 95% β 75% β

  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 0602 Nantou earthquakes have similar rupture scenarios.

  20. 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

  21. Thanks for your attention.

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