An Improved Method to Determine Coda-Q, Earthquake Magnitude, and Site Amplification: Theory and Application to Southern California

Wei Wang, & Peter M. Shearer

Published August 13, 2017, SCEC Contribution #7543, 2017 SCEC Annual Meeting Poster #073

The wavetrain following direct P and S is called the coda and is caused by scattered energy. Coda waves play an important role in seismology for measuring the attenuation of media, earthquake magnitude, and site amplification. We have developed an improved multi-station and multi-event method (MSMEM) to determine these three important seismic parameters simultaneously. We analyze 621 representative local (< 100 km) and shallow (< 20 km) earthquakes with catalog magnitudes from 1.8 to 5.4 in southern California at multiple frequency bands centered at 1.5, 3, 6, and 12 Hz. We find that the length of the moving average time window can affect the measurement of coda attenuation Q_C, but our tests indicate that the optimal window length is about 15 times the dominant data period. We use linear regression to fit each coda section and use only those portions that agree with the model decay rate with a correlation coefficient larger than 0.9. Our results indicate that the estimated frequency-dependent coda-Q (Q_C=Q_0 f^a) at 1 Hz (Q_0) and the power a-value ranges are 110--305 and 0.69--1.49, respectively. Our coda magnitude estimates are linearly correlated with catalog magnitude and calibrated to moment with b-value 1.30, and our observed lateral variations in coda-Q and our site amplification factors are in general agreement with previous results, although there are notable differences at some locations. Our results suggest that this approach provides a unified, accurate and stable method to measure coda-Q, earthquake magnitude, and site amplification using coda waves of locally recorded earthquakes.

Key Words
Coda-Q, Site Amplification, Coda Magnitude

Citation
Wang, W., & Shearer, P. M. (2017, 08). An Improved Method to Determine Coda-Q, Earthquake Magnitude, and Site Amplification: Theory and Application to Southern California. Poster Presentation at 2017 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology