Localization of background seismicity: Estimation and application to tracking preparation of large earthquakes - Livestream

Progressive localization of deformation is a basic mechanical process that produces simultaneously reduced strength and increasing strain in a deforming rock volume. The localization framework describes the progressive evolution of deformation from distributed failures in a rock volume to localized shear zones, culminating in generation of primary slip zones and large earthquakes [2]. This framework considers the development of conditions during deformation in a volume (rather than on pre-existing faults or sets of faults) that allow an appropriate “trigger” to produce large ruptures. Recent observations provide new promising perspectives related to observable localization signals preceding large earthquakes. This talk discusses estimation of localization using earthquake catalogs and its applications to tracking preparation processes of large earthquakes [1]. The estimation methodology is based on comparing “spikiness” of spatial measures using the Relative Operating Characteristic (ROC) approach. The comparison is done both between space distributions of observed background events within distinct time windows (relative localization), and between an observed space distribution and a uniform measure with the same support (absolute localization). We also discuss a nearest-neighbor methodology for earthquake delcustering, which is an essential component of our (and many other) analyses of earthquake catalogs [3]. The results reveal generation of earthquake-induced rock damage on a decadal timescale around eventual rupture zones, and progressive localization of background seismicity on a 2-3 yr timescale before several M > 7 earthquakes in southern and Baja California, and M7.9 events in Alaska. This is followed by coalescence of earthquakes into growing clusters that precede the mainshocks. Corresponding analysis around the 2004 M6 Parkfield earthquake in the creeping section of the San Andreas fault shows opposite tendencies to those associated with the large seismogenic faults. The results are consistent with observations from laboratory experiments and physics-based models with heterogeneous materials not dominated by a pre-existing failure zone.

Speaker: Ilya Zaliapin, University of Nevada, Reno

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