Source radiation invariant property of local and near!regional shear!wave coda: Application to source scaling for the Mw 5.9 Wells, Nevada sequence

Abstract

This study documents another unique property of local and regional shear!wave coda: that scattering in the Earth’s crust averages out source heterogeneities such as focal mechanism and directivity. We consider two recent events which exhibited significant source directivity. The first, an Mw 4.2 Oakland hills, California strike!slip event on July 20, 2007, resulted in uncharacteristically large amounts of damage in the Montclair and south Berkeley neighborhoods, along strike and north!west of the hypocenter, but almost no damage to the south!east. The second event, the Mw 5.9 Wells, Nevada dip!slip event of February 21, 2008, was well!recorded by the Earthscope Transportable Array (USArray) and determined to exhibit south!west directivity. We conclude with an example of corner!frequency ( fc) estimates from the Wells sequence, which showcase the coda’s low variance, and find that scaling is non!self!similar, suggesting a change in dynamics between the mainshock and aftershocks.