Detecting Small Earthquakes on Remote Oceanic Transform Faults
Thursday, 18 December 2014
Although oceanic transform faults (OTF) 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. The large fraction of aseismic deformation that accompanies OTF earthquakes also 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 these 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 rgarding rupture length and area as well as rupture-front propagation speed remain unknown in these systems. Even identifying the smaller-magnitude activity that often provides clues to some of these quantities is difficult. Short-period seismic arrays at least occasionally provide information suitable for locations of small (mb < 4.0) earthquakes along Mid-Atlantic transforms such as the Romanche and Chain. In this work, we explore the possibility of detecting smaller earthquakes along remote OTFs using waveform-based comparisons (e.g. cross correlations) of template signals with the continuous seismic wavefield for seismic stations surrounding several OTFs. We examine our ability to detect these small events using a range of frequency bands from short-to-intermediate periods and investigating effective approaches for identifying small-magnitude events along remote OTFs. Preliminary results suggest that at least some small events can be identified using simple 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 and allow us to continue to investigate OTF deformation processes using remote seismic observations.