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The Time-saturation of Tectonic Tremor With Low-frequency Earthquakes

Description: 

The low-frequency earthquakes (LFEs) that make up much or all of tectonic tremor are often interpreted as resulting from the acceleration and then deceleration of slip on isolated portions of the plate interface. This allows one to estimate the moment and duration of individual LFEs, leading to inferences of their magnitude-frequency and moment-duration relations. However, in existing stochastic models of tremor generation, what we call “an LFE” instead represents the superposition of numerous concurrent accelerations and decelerations of slip in distinct locations, as modified by different source-station travel times. Attributes of tremor seismograms from southern Vancouver Island suggest the latter view.

Here we examine inter-event times in an LFE catalog derived in Song & Rubin (2025) by deconvolving continuous tremor records with empirical Green's functions, the latter made from stacks of cataloged LFEs belonging to a single LFE family. Over time windows as large as a few seconds, the catalog contains detections for each consecutive peak in the seismograms, which occur at a rate of approximately 4 per second. This renders it doubtful that each detection represents just a single LFE. Across a 6-fold range of amplitude, tremor often appears to be saturated with LFE arrivals in this way, meaning that on average their temporal separation is no larger than the characteristic LFE duration. Quiet tremor differs from loud tremor most obviously in that the time delay between clustered detections continually increases as tremor amplitude decreases. If saturation is a general characteristic of tremor, it may render LFE magnitude-frequency and moment-duration relations essentially unknowable with existing data. If, in addition, LFEs are drawn from a time-invariant magnitude-frequency distribution, much of the seismic moment is “missing” from the standard tremor passband. While saturation-corrected LFE moment need not violate the geodetic limit, it leaves little room for aseismic slip, which may be incompatible with the mechanical heterogeneity type of LFE models where a large fraction of the fault slips aseismically.

Session: Predictability of Seismic and Aseismic Slip: From Basic Science to Operational Forecasts - I

Type: Oral

Date: 4/16/2025

Presentation Time: 04:30 PM (local time)

Presenting Author: Chao

Student Presenter: No

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