Moment Rate Spectra using 2-D Path Correction

Abstract:

Estimating moment magnitudes using coda waves has proven to be one of the most robust measurements of the size of an earthquake. In most regions, moderate to large size earthquakes can be easily calibrated with 1-D regional path correction of coda waves at low frequencies (f < 0.5 Hz). Above a certain frequency (f > 0.5 Hz) a larger scattering is observed which leads to higher variation for smaller earthquakes which are only recorded at these higher frequencies. Lawrence Livermore National Laboratory has been improving the number of coda envelope measurements in the Middle East due to significant developments of seismic networks and the recent deployments. We use more than 2000 earthquakes recorded by nearly 60 broad-band stations to investigate the 2-D propagation effects of the coda waves. We have found that coda waves have substantially different propagation properties than the direct waves, and these differences need to be accounted for in the tomographic inversion. The tomographic method separates and simultaneously inverts the Sn-coda and Lg-coda phases for Q over a frequency range of 0.3 to 8 Hz. Initial results of 2-D Q maps are very similar to the direct wave attenuation maps at certain frequencies.