Static Source Properties of Slow and Fast Earthquakes

Abstract

The source characteristics of slow and fast earthquakes provide a window into the mechanical properties of faults. In particular, the average stress drop controls the evolution of friction, fault slip, and event magnitude. However, this important source property is typically inferred from the analysis of seismic waves and is subject to many epistemic uncertainties. Here, we investigate the source properties of 53 earthquakes and 17 slow-slip events on thrust and strike-slip faults in various tectonic settings using slip distributions constrained by geodesy in combination with other data. We determine the width, potency, and potency density of slow and fast earthquake sources based on static slip distributions. The potency density, defined conceptually as the ratio of average slip to rupture radius, is a measure of anelastic deformation with limited bias from rigidity differences across depths and tectonic settings. Strike-slip earthquakes have the highest potency density, varying from 20 to 500 microstrain. The potency density is on average lower on continental thrust faults and megathrusts, from 10 to 200 microstrain, with an algebraic decrease with centroid depth, indicative of systematic changes in dominant rupture processes with depth. Slow slip events represent an end-member style of rupture with low potency density and large rupture width. Significant variability in potency density of slow-slip events affects their moment-duration scaling. The variations of source properties across tectonic settings, depth, and rupture styles can be used to better constrain numerical simulations of seismicity and to assess the source characteristics of future earthquakes and slow slip events. Plain Language Summary Natural earthquakes reduce the stress that accumulates on faults due to plate tectonics. To better understand the variability of seismic hazards around active faults, we survey the properties of slow and fast earthquakes around the world. The potential of faults to concentrate large slip in the rupture area differs depending on the geological setting, the depth of the source, and the type of rupture. Earthquakes in a continental setting condense more slip in a given rupture area, particularly in transform faults like the San Andreas fault. Subduction zone earthquakes, although some of the largest events on Earth, generally distribute less slip over a wider area, but this varies as a function of depth. Slow earthquakes represent an extreme case of little slip distributed over a large area. The propensity of rupture characteristics to vary with fault type and depth may help forecast the hazards posed by future seismicity.

Coseismic Folding During Ramp Failure at the Front of the Sulaiman Fold‐and‐Thrust Belt

“…For the backward‐vergent models, flexural slip only occurs near the up‐dip tip of the ramp rupture, and coseismic slip is mostly confined on the frontal ramp, with the maximum slip of 50 and 45 cm found at 7.0 km depth respectively (Figures 3b and 3d). The potency density, that is, the stress drop scaled by the rigidity of the host rocks (see Text S3 in Supporting Information ), is 44 micro‐strain, consistent with that of thrust‐earthquakes in the region and worldwide (Nanjundiah et al., 2020).…”

Detection of “Rapid” Aseismic Slip at the Izu‐Bonin Trench

“…See also Nanjundiah et al. (2020) for the variety of source durations of slow slip events. Clearly, more work is needed to resolve the issue.…”

“…Ide et al (2007Ide et al ( , 2008 and Ide (2014), on the other hand, argued for the real gap between the fast and slow slip modes which follow mutually distinct scaling laws. See also Nanjundiah et al (2020) for the variety of source durations of slow slip events. Clearly, more work is needed to resolve the issue.…”

Period‐Multiplying Cycles at the Transition Between Stick‐Slip and Stable Sliding and Implications for the Parkfield Period‐Doubling Tremors

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Shear failure on natural faults includes a wide range of rupture styles with slip velocities ranging from nanometer to meter per second (Beroza & Ide, 2011). Slow-slip events provide new opportunities to study fault mechanics because of their relatively short recurrence time associated with low stress drops (Nanjundiah et al, 2020). Slow-slip events are often accompanied by low-frequency earthquakes and tremors, but the relationship between the long, sluggish rupture of slow-slip events and the rapid seismic radiation of low-frequency earthquakes and tremors remains enigmatic.

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