Slow slip events and seismic tremor at circum‐Pacific subduction zones

Abstract

It has been known for a long time that slip accompanying earthquakes accounts for only a fraction of plate tectonic displacements. However, only recently has a fuller spectrum of strain release processes, including normal, slow, and silent earthquakes (or slow slip events) and continuous and episodic slip, been observed and generated by numerical simulations of the earthquake cycle. Despite a profusion of observations and modeling studies the physical mechanism of slow slip events remains elusive. The concurrence of seismic tremor with slow slip episodes in Cascadia and southwestern Japan provides insight into the process of slow slip. A perceived similarity between subduction zone and volcanic tremor has led to suggestions that slow slip involves fluid migration on or near the plate interface. Alternatively, evidence is accumulating to support the notion that tremor results from shear failure during slow slip. Global observations of the location, spatial extent, magnitude, duration, slip rate, and periodicity of these aseismic slip transients indicate significant variation that may be exploited to better understand their generation. Most slow slip events occur just downdip of the seismogenic zone, consistent with rate‐ and state‐dependent frictional modeling that requires unstable to stable transitional properties for slow slip generation. At a few convergent margins the occurrence of slow slip events within the seismogenic zone makes it highly likely that transitions in frictional properties exist there and are the loci of slow slip nucleation. Slow slip events perturb the surrounding stress field and may either increase or relieve stress on a fault, bringing it closer to or farther from earthquake failure, respectively. This paper presents a review of slow slip events and related seismic tremor observed at plate boundaries worldwide, with a focus on circum‐Pacific subduction zones. Trends in global observations of slow slip events suggest that (1) slow slip is a common phenomena observed at almost all subduction zones with instrumentation capable of recording it, (2) different frictional properties likely control fast versus slow slip, (3) the depth range of slow slip may be related to the thermal properties of the plate interface, and (4) the equivalent seismic moment of slow slip events is proportional to their duration (Moατ), different from the Moατ3 scaling observed for earthquakes.

Scaling Relationships of Source Parameters for Slow Slip Events

“…Note that there is a lack of observations in our dataset for seismic moment within ∼1:0e15 1:0e17 N·m corresponding to duration ranging from minutes to days. A similar analysis was performed by Schwartz and Rokosky (2007) and Peng and Gomberg (2010), where the latter consider a broader class of aseismic phenomenon. The Cascadia SSEs, a slow earthquake sequence , and short-term SSEs (Sekine et al, 2010) all fall within the LogM 0 ∼ LogT trend.…”

“…Slow earthquakes have also been reported in other tectonic environments such as the San Andreas fault (Linde et al, 1996) and Hawaii (Segall et al, 2006;Montgomery-Brown et al, 2009). Although several hypotheses have been proposed to explain these events (e.g., Ito et al, 2007;Schwartz and Rokosky, 2007;Brodsky and Mori, 2007;Ide, 2008;Liu and Rice, 2009;Ando et al, 2010;Hawthorne and Rubin, 2010;Ide, 2010;Liu and Rubin, 2010;Peng and Gomberg, 2010;Shibazaki et al, 2010), the physical mechanisms are still not fully understood.…”

“…This difference in the scaling prompted Ide et al (2007) to describe slow slip, tremor, and lowfrequency earthquakes as representing a unique physical process distinct from that of earthquakes. Schwartz and Rokosky (2007) also noted the distinct moment-duration *Now at the Seismology Laboratory, University of Rhode Island. relationship of SSEs.…”

Seismic variability of subduction thrust faults: Insights from laboratory models

“…The interplate contact is seismogenic only in a specific depth interval [Scholz, 1998], which globally is comprised between 11 ± 4 km and 51 ± 9 km (Figures 1a and 1b). In several subduction zones, slow slip events are recognized downdip of the limit of the seismogenic zone, even if their physical mechanism still remains elusive [e.g., Schwartz and Rokosky, 2007;Gomberg et al, 2010]. Moreover, cumulative seismic moment (M′) is not homogeneously distributed along the seismogenic zone, but shows an approximately Gaussian distribution with a peak around 20-30 km of depth (Figure 1c).…”

Tectonic tremors could offer insights into the big shakers

“…These slow-slip earthquakes can be found around the globe, primarily in subduction zones, places where one tectonic plate is diving beneath another (6). The most destructive earthquakes occur in subduction zones located in places such as Chile, Japan, Alaska, Washington state, and British Columbia.…”