Spatial distribution and energy release of nonvolcanic tremor at Parkfield, California

Abstract

Nonvolcanic tremors (NVTs) are observed in transition zones between freely slipping and locked sections of faults and normally occur below the seismogenic zone. Based on NVT recordings in the Parkfield region of the San Andreas Fault, we provide a novel approach to assess the energy release of these events and assign magnitudes (Me) that are compatible with size estimates of small earthquakes in the same region. To assess the energy magnitude of a detected tremor, we refine the estimate of its duration and perform a spectral analysis that accounts for local attenuation. For the 218 NVTs that we were able to process, we resolve Me values in the range of −0.67 to 0.84. For events, which we could not process using the spectral analysis technique, we propose a statistical model to estimate Me values using observable characteristics, such as peak amplitude, spectral velocity at the source corner frequency, and duration. We furthermore provide seismic moment and moment magnitude estimates and calculate stress drops in a range of 3–10 kPa. As a result of our spectral analyses, we find strong indications regarding the ongoing debate about potential NVT location hypotheses: the Parkfield NVTs have a higher probability to be located in the proposed three‐dimensional cloud‐like cluster than in any other suggested location distribution.

Cataloging Tectonic Tremor Energy Radiation in the Cascadia Subduction Zone

“…Energy has been previously used in tremor studies to assign magnitudes to tectonic tremor along the San Andreas Fault (Staudenmaier et al., 2016) and western Japan (Mizuno & Ide, 2019) using Choy and Boatwright (1995)'s relationship above. However, this empirical relationship was formulated using surface wave magnitudes of 378 moderate‐to‐large earthquakes ( M S > 5) globally, potentially limiting its relevance and applicability to low‐amplitude tremor.…”

“…The lack of observable low frequencies makes it difficult to estimate seismic moment. Numerous previous studies have used seismic energy (Ando et al., 2012; Ide et al., 2008; Maeda & Obara, 2009; Staudenmaier et al., 2016; Yabe & Ide, 2014) to estimate the size of tremors in various subduction zones, and energy has been shown to radiate heterogeneously along these megathrust interfaces (e.g., Baba et al., 2020; Maeda & Obara, 2009; Yabe & Ide, 2014).…”

The source scaling and seismic productivity of slow slip transients

“…However, when considering tremor, it is not possible to calculate seismic moments, except in particular cases ( 22 ). The magnitude of LFEs is not routinely estimated; there is an exception, however, such as the LFE catalog published by the Japan Meteorological Agency (JMA) ( 25 ) and a few specific published case studies ( 58 , 59 ). A valuable and promising source for slow slip transient processes is the recently published Slow Earthquake Database (http://www-solid.eps.s.u-tokyo.ac.jp/~sloweq/) ( 24 ), which contains many cases of slow slip phenomena studied using seismological and geodetic investigations.…”

Bilinearity in the Gutenberg‐Richter Relation Based on ML for Magnitudes Above and Below 2, From Systematic Magnitude Assessments in Parkfield (California)

“…We therefore restrict our data set to the recordings of a single reference station: Stockdale Mountain Borehole. The station is the third deepest in the HRSN, with the sensor depth of 282 m below the surface and was selected due to very low noise and undisturbed recording over long periods (Staudenmaier et al, ).…”