2012 IRIS Workshop
Quantifying Tectonic Tremor in Southern Mexico and its Curious Relationship to Slow Slip, Earthquakes, and other Tremor Triggers
Stefany M. Sit: Miami University, Michael R. Brudzinski: Miami University
Results of a single station tremor detection algorithm using frequency ratios applied in Oaxaca, Mexico. Tremor is detected over a 14-month time span using the ratio method (red), mean amplitude processing (orange), and semi-automated source location (circles). Frequency ratios detect more episodes and more clearly identifies them. Unlike in Cascadia, tremor activity does not last longer than a week nor does it increase during a geodetically observed multi-month SSE (purple).
Full-resolution graphics file in original format: 0075.jpg
The Oaxaca subduction zone is an ideal region to study plate boundary deformation, where we have a multi-year record of tectonic tremor detections and slow slip observations prior to the recent Mw 7.4 megathrust earthquake on March 12, 2012. To detect tectonic tremor, we take advantage of its narrow frequency content by calculating a ratio of amplitudes in the tremor passband relative to amplitudes in higher and lower frequency passbands where regional seismicity and surface waves are more common, respectively. Application of this recently developed technique allows us to quickly examine the prevalence of tremor over long time frames, where we have as of yet found no reliable correlation between tremor and geodetically detected slow slip. This result was surprising considering that tremor and slip are so well correlated in Cascadia that a linear relationship exists between the number of tremor hours recorded and the moment of concurrent slow slip [e.g., Aguiar et al, 2010]. The unusual relationship between tremor and slow slip in Oaxaca furthered our interests to investigate whether tremor can be tidally modulated or teleseismically triggered, as recent modeling has indicated such a triggering relationship could be used to examine the state of stress and frictional properties on the fault interface.
Acknoweldgements: NSF Award#0847688
Keywords: episodic_tremor_and_slip, event_detection, frequency_analysis, mexico, subduction_zones
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