Moment Magnitudes of Local/Regional Events from 1D Coda Calibrations in the Broader Middle East Region [Moment Magnitudes of Small to Moderate Size Regional Events from Coda Calibration in the Broader Middle East]

Journal Article · Tue Sep 13 00:00:00 EDT 2016 · Bulletin of the Seismological Society of America

DOI:https://doi.org/10.1785/0120160045· OSTI ID:1466161

Gök, Rengin ^[1]; Kaviani, Ayoub ^[2]; Matzel, Eric M. ^[1]; Pasyanos, Michael E. ^[1]; Mayeda, Kevin ^[3]; Yetirmishli, Gurban ^[4]; El‐Hussain, Issa ^[5]; Al‐Amri, Abdullah ^[6]; Al‐Jeri, Farah ^[7]; Godoladze, Tea ^[8]; Kalafat, Dogan ^[9]; Sandvol, Eric A. ^[10]; Walter, William R. ^[1]

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1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
2. Goethe University of Frankfurt (Germany). Institute of Geosciences
3. Univ. of California, Berkeley, CA (United States). EECS
4. Republican Seismic Survey Center of Azerbaijan National Academy of Sciences, Baku (Azerbaijan). Azerbaijan National Academy of Sciences
5. Sultan Qaboos University, Al Khoud (Sultanate of Oman). Earthquake Monitoring Center
6. King Saud Univ., Riyadh (Saudi Arabia)
7. Kuwait Institute of Scientific Research, Kuwait City (Kuwait)
8. Ilia State University, Tbilisi (Georgia)
9. Boğaziçi University, Istanbul (Turkey). Kandilli Observatory and Earthquake Research Institute
10. Univ. of Missouri, Columbia, MO (United States). Department of Geological Sciences

Reliable moment magnitude estimates for seismic events in the Middle East region can be difficult to obtain due to the uneven distribution of stations, the complex tectonic structure, and regions of high attenuation. In this paper, we take advantage of the many new broadband seismic stations that have become available through improved national networks and numerous temporary deployments. We make coda envelope-amplitude measurements for 2247 events recorded by 68 stations over 13 narrow frequency bands ranging between 0.03 and 8 Hz. The absolute scaling of these spectra was calculated based on independent waveform modeling solutions of the moment magnitudes for a subset of these events to avoid circularity. Using our 1D path calibrations, we determined coda-based magnitudes for a majority of the events. We obtain fairly good agreement with waveform-modeled seismic moments for the larger events (Mw>4.5) at low frequencies (<0.7 Hz). As expected, the coda-derived source spectra become increasingly scattered at higher frequencies (>0.7 Hz) because of unaccounted 2D path effects, as well as mixing of both Sn coda and Lg coda, which have different attenuation behavior. This scatter leads to increased variance in the magnitudes estimated for smaller events in which low-frequency amplitudes are below the noise levels and the higher frequencies are the only signals available. We quantify the expected variance in coda envelope amplitudes as a function of frequency using interstation scatter as our metric. Finally, the net results of this study provide thousands of new 1D coda magnitude estimates for events in the broad region, as well as the necessary initial starting model for use in a new related 2D coda study (Pasyanos et al., 2016).

• Research Organization: Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: AC52-07NA27344
• OSTI ID: 1466161
• Report Number(s): LLNL-JRNL--679299; 803224
• Journal Information: Bulletin of the Seismological Society of America, Journal Name: Bulletin of the Seismological Society of America Journal Issue: 5 Vol. 106; ISSN 0037-1106
• Publisher: Seismological Society of America
• Country of Publication: United States
• Language: English

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58 GEOSCIENCES