2D Variations in Coda Amplitudes in the Middle East

Abstract

Coda amplitudes have proven to be a stable feature of seismograms, allowing one to reliably measure magnitudes for moderate‐to‐large ( M ≥3) earthquakes over broad regions. Because smaller ( M <3) earthquakes are only recorded at higher frequencies for which we find larger interstation scatter, amplitude and magnitude estimates for these events are more variable, regional, and path dependent. In this article, we investigate coda amplitude measurements in the Middle East for 2D variations in attenuation structure. One critical aspect of this effort is characterizing the propagation term to include scattering, which allows us to use amplitudes out to longer distances and later in the coda. We perform a tomographic inversion and find that the recovered attenuation structure is both very similar to the attenuation structure derived from direct phases and also reflective of the tectonic structure of the region. We then apply the 2D attenuation corrections to several hundred events in the region and find marked improvements to our magnitude estimates, as measured by interstation scattering, resulting in standard deviations of less than 0.025 magnitude units at all frequencies. The improvements are greatest at high frequencies, which will have the largest effect on smaller magnitude events.