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- Title
Are Low‐Frequency Earthquake Moments Area‐ or Slip‐Limited? A Rock Record Examination.
- Authors
Williams, Randolph T.; Kirkpatrick, James D.
- Abstract
The seismic moments observed for low‐frequency earthquakes (LFEs) vary over multiple orders of magnitude, even where the LFEs occur within families of similar events. Although this variability is typically interpreted to record a scale‐limited process at the LFE source, neither the slip per LFE nor the rupture area can be determined from seismological constraints. Here, we examine incrementally developed slickenfibers that have been proposed to record LFEs in exhumed subduction zones. These structures form through repeated, micron‐scale slip events across dilational irregularities in the fault plane, which are punctuated by cementation and sealing in the interstitial space. By statistically analyzing the geometry of inclusion trails delineating slip‐parallel mineral‐growth increments, we constrain the variability in slip per inferred LFE and test end‐member hypotheses regarding the controls on LFE moments. We find that that the slickenfibers exhibit characteristic slip increments, favoring a "slip‐limited" model that requires large variability in LFE rupture areas. Plain Language Summary: Low‐frequency earthquakes (LFEs) are a category of seismic phenomena only perceptible by geophysical instruments. Understanding what causes these events, however, may help us understand larger magnitude earthquakes occurring along plate boundaries. Unfortunately, the physical processes that generate LFEs at their source depth are poorly understood. Seismological studies have shown that energy release varies substantially from one LFE to another, for example, but the causes of this variability are unclear. Given that energy release is proportional to the area of LFE rupture and the slip during the LFE, a common conceptual model argues that the variability in LFE energy release results from a wide variation in slip amount occurring over a relatively constant area between events. We utilize a unique record of slip events extracted from geological structures (inferred to record ancient LFEs) to test competing models governing energy release at the LFE source. Using a statistical test that quantifies the variability of slip increment recorded in rock samples, we find that the amount of slip during individual inferred LFEs has a strong preferred value with little variation between events. This result indicates variations in LFE energy release are determined primarily by variations in the area over which the slip occurs. Key Points: We examine slip increments associated with LFE structures in geological exposuresStatistical analysis shows that the slicken fibers record characteristic slip incrementsResults indicate slip‐limited seismic moments during low frequency earthquakes
- Subjects
SOUND recordings; GEOPHYSICAL instruments; EARTHQUAKES; SEISMOGRAMS; CONCEPTUAL models; MAGNITUDE (Mathematics); EARTHQUAKE magnitude; SUBDUCTION zones
- Publication
Geophysical Research Letters, 2022, Vol 49, Issue 2, p1
- ISSN
0094-8276
- Publication type
Article
- DOI
10.1029/2021GL095759