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Near-field strong ground-motion data from the September 12-13, 2007 Sumatra sequence

Near-field strong ground-motion data from the September 12-13, 2007 Sumatra sequence. Preliminary report by Hudnut, K., J. Galetzka, K. Sieh, C. Stephens, D. Boore, A. Acosta, J. Genrich, T. Heaton, J. Yang, R. Briggs, A. Borsa and K. Stark U53A-05 Fall AGU Meeting

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Near-field strong ground-motion data from the September 12-13, 2007 Sumatra sequence

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  1. Near-field strong ground-motion data from the September 12-13, 2007 Sumatra sequence Preliminary report byHudnut, K., J. Galetzka, K. Sieh, C. Stephens, D. Boore, A. Acosta, J. Genrich, T. Heaton, J. Yang, R. Briggs, A. Borsa and K. Stark U53A-05 Fall AGU Meeting San Francisco, California December 14, 2007

  2. Acknowledgments • Caltech Tectonics Observatory • Jean-Philippe Avouac, Director; Kerry Sieh, Sumatra Lead • Tom Heaton (K2’s), Don Helmberger, Hiroo Kanamori, Rob Clayton • Jeff Genrich, John Galetzka, Rich Briggs, Aron Meltzner, Ozgun Konca, Anthony Sladen, Willy Amidon, Keith Stark (consultant) • LIPI • Danny Natawidjaja • UCSD/SOPAC • Linette Prawirodirjo, Peng Fang, Yehuda Bock • U. S. Geological Survey • Walter Mooney, IOTWS Lead for USGS; Bill Ellsworth - advocacy & support • Ron Porcella (K2’s), Arnie Acosta, Chris Stephens, Dave Boore, Roger Borcherdt, Shane Detweiler, Woody Savage, Mehmet Celebi, Adrian Borsa

  3. Engineering seismology Earthquakes <600 km from Jakarta, Singapore, and Kuala Lumpur PADANG - tsunami threat JAKARTA

  4. Pulau Sikuai - PSKI From Chris Stephens, USGS Menlo Park For the Mw 8.4 at 392 km (horizontal components combined): PGA horiz. of 55.97 cm/s2 ; ~6% g (not ‘huge’) PGV 5.9 cm/s horiz. ; -3.5 cm/s vert. For the Mw 7.9 at 165 km (horizontal components combined): : PGA horiz. of 168.4 cm/s2 ; ~17.2% g (still not ‘huge’) PGV 11.3 cm/s horiz. ; -6.8 cm/s vert. Long-Period Energy? Directivity effects?

  5. Preliminary finite-fault source modelsProf. Chen Ji, UCSB - M 8.4 & Yuehua Zeng, USGS - M 7.9 PSKI SLBU Thanks to Rich Briggs for the KML files

  6. PSKI - Event 1 - Mw 8.4 Velocity records for the Mw 8.4 (by Dave Boore)

  7. ShakeMap Ground-Motion Prediction PGV: ~10 cm/s at Padang (computed) 6.9 cm/s (observed) Automated - based on Wald et al. (2005) and finite-fault source model by Chen Ji

  8. PSKI - Event 2 - Mw 7.9 Velocity records for the Mw 7.9 (by Dave Boore) note: data are un-filtered

  9. PSKI photograph Courtesy of John Galetzka; Caltech Tectonics Observatory Enclosure and solar array act as an inverted pendulum at 3-5 Hz & ~20 Hz

  10. Silabu (SLBU) station photos Courtesy of John Galetzka; Caltech Tectonics Observatory Much closer than PSKI Data received from JEG on October 2 • Chris Stephens ran into problems with the data • Data from M 8.4 - P-wave is missing • Data from M 7.9 - record had to be spliced • Still evaluating data - initial plots made yesterday Enganno data not yet retrieved from field. Siberut had a power malfunction and did not record data.

  11. SLBU Waveforms for the Mw 8.4 (by Chris Stephens) note: data are un-filtered

  12. SLBU Spliced record for the Mw 7.9 (by Chris Stephens) Three pulses of energy - Burst 1 @ 5-25 sec Burst 2 @ 35-60 sec Burst 3 @ 70-90 sec 1 2 3

  13. Data processing, archiving & distribution http://www.strongmotioncenter.org/ NSMP Data Center & NCESMD partnership Open data policy is key http://nsmp.wr.usgs.gov/ GPS and accelerometer data are complementary A robust system will likely require both for redundancy

  14. Conclusions • Strong-motion data from K2’s at PSKI and SLBU were recorded for the Mw 8.4, Mw 7.9, and several smaller events • Results are within expectations for the Mw 8.4 at Padang • Surprisingly sharp onset of Mw 7.9 noticed in teleseismic data by others; strong-motion data confirm this and provide higher resolution near field recordings • K2 data have problems with reliable recording of large motions • GPS data appear to be noisier overall, but reliably record large dynamic and static displacements (K2’s failed to do this) • Most important result of these data is likely the initial pulse of the Mw 7.9 because of its implications about earthquake nucleation process; very rapid (<5-10 sec) large slip (5-7 m). Also, strong-motion data show three pulses rather than only two seen teleseismically. • Co-located GPS data will be reported in the next presentation by Genrich et al., then comparisons and earthquake source models will be given by Konca et al.

  15. by John Galetzka, Caltech Tectonic Observatory

  16. Backup Slides

  17. SLBU Velocity for Mw 8.4 ~80 cm/sec broad pulse note: data are un-filtered

  18. SLBU Displacement for Mw 8.4 Approx. 10x larger than from GPS from Peng Fang (static) and Jeff Genrich (kinematic) - all results preliminary note: data are un-filtered

  19. Place-holder: Ozgun & Jeff

  20. PSKI - Event 1 - Mw 8.4 Waveforms for the Mw 8.4 (by Chris Stephens)

  21. PSKI - Event 2 - Mw 7.9 Waveforms for the Mw 7.9 (by Chris Stephens)

  22. PSKI - Event 3 - Mw 7.0 Waveforms for the Mw 7.0 (by Chris Stephens)

  23. PSKI - Event 3 - Mw 7.0 Waveforms for the Mw 7.0 (by Dave Boore)

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