Detecting and Locating Small Earthquakes Along Remote Oceanic Transform Faults

Abstract:

Although oceanic transform faults (OTFs) constitute a small fraction of the total plate boundary area, better constraints on OTF tectonic parameters (e.g. fault length, slip rate, thermal structure) compared to other tectonic boundaries make OTFs a useful focus of the investigation of earthquake processes. OTF earthquakes are also accompanied by a large fraction of aseismic deformation that makes them an interesting target for exploring the interaction of creep with slow and quick earthquakes. Because most typical OTFs are quite remote, even indirectly observing their deformation processes is a serious challenge. Standard teleseismic analysis methods have yielded valuable constraints on the first-order characteristics of moderate-to-large magnitude OTF earthquakes, but fundamental questions regarding rupture length and area as well as rupture-front propagation speed remain unknown in these systems; Identifying the smaller-magnitude activity that often provides insight to some of these quantities is difficult. Short-period seismic arrays occasionally provide adequate information needed to locate small (mb < 4.0) earthquakes along Mid-Atlantic transforms. In this work, we explore the possibility of detecting and locating smaller earthquakes along remote OTFs using intermediate-period waveform-based comparisons (e.g. cross correlations) of template signals with the continuous seismic wavefield observed at seismic stations surrounding several OTFs. To extend our application to regions with limited template signals, we employ the match and locate procedure of Wang and Wen (2015) and use a spatial grid search to identify the location that maximizes network cross-correlation values. Preliminary results suggest that at least some small events can be identified and located using moderate-magnitude waveform templates. Our goal is to construct a metric that will produce acceptable false-alarm rates and that will allow us to visually confirm detections and extend the seismicity catalogs along OTFs to lower magnitude threshold, helping us to continue to investigate OTF deformation processes using remote seismic observations.