Coda Magnitudes of Small Events in Iran and Surrounding Regions
Abstract
Seismic coda envelope techniques provide a means of determining accurate moment magnitudes for earthquakes that are too small to easily be fit using waveform modeling techniques. Using the dense coverage of the Iranian broadband stations, we calculated the moment magnitudes of small events ( mb > 3.5 ) using coda calibrated envelopes. 17 broad-band stations equipped with CMG-3T sensors recorded more than 6000 regional events. This data provided excellent coverage to improve coda peak, shape and path parameters in the region. First, we analyzed coda envelopes for 13 narrow frequency bands to estimate coda shapes and peak velocities. This addresses the regional variation of wave propagation. In particular, there are large differences between the high frequency envelopes for the events recorded from Pakistan, Caspian Sea and Arabian Platform. Accounting for this allows us to extend our capabilities to smaller magnitudes and higher frequencies. To enhance the data quality, we strictly examined the envelopes for any spikes, aftershocks or peculiar onsets. Second, we obtained coda amplitudes at each calibrated region and merged with other data in the region. The new data set provided coverage to map out 2-D path effects, which decrease the magnitude variance of the estimates from different stations dramatically. We aim to analyze smaller events (down to mb=3.0 ) as we improve our measurements at each step. This data will also provide a source for 2-D coda-shape and coda-peak parameter calculation where the improved coda amplitudes will be measured. We compare coda magnitudes with waveform modeled Mw's where we find very good agreement for larger magnitude events (Mw > 4.5).
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.S44C..08G
- Keywords:
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- 7215 SEISMOLOGY / Earthquake source observations;
- 7218 SEISMOLOGY / Lithosphere