Delayed Seismicity Rate Changes Controlled by Static Stress Transfer

Abstract

On 15 June 2010, a Mw5.7 earthquake occurred near Ocotillo, California, in the Yuha Desert. This event was the largest aftershock of the 4 April 2010 Mw7.2 El Mayor‐Cucapah (EMC) earthquake in this region. The EMC mainshock and subsequent Ocotillo aftershock provide an opportunity to test the Coulomb failure hypothesis (CFS). We explore the spatiotemporal correlation between seismicity rate changes and regions of positive and negative CFS change imparted by the Ocotillo event. Based on simple CFS calculations we divide the Yuha Desert into three subregions, one triggering zone and two stress shadow zones. We find the nominal triggering zone displays immediate triggering, one stress shadowed region experiences immediate quiescence, and the other nominal stress shadow undergoes an immediate rate increase followed by a delayed shutdown. We quantitatively model the spatiotemporal variation of earthquake rates by combining calculations of CFS change with the rate‐state earthquake rate formulation of Dieterich (1994), assuming that each subregion contains a mixture of nucleation sources that experienced a CFS change of differing signs. Our modeling reproduces the observations, including the observed delay in the stress shadow effect in the third region following the Ocotillo aftershock. The delayed shadow effect occurs because of intrinsic differences in the amplitude of the rate response to positive and negative stress changes and the time constants for return to background rates for the two populations. We find that rate‐state models of time‐dependent earthquake rates are in good agreement with the observed rates and thus explain the complex spatiotemporal patterns of seismicity.

Fracture Advancing Step Tectonics Observed in the Yuha Desert and Ocotillo, CA, Following the 2010 Mw7.2 El Mayor‐Cucapah Earthquake

“…On 15 June 2010, 71 days after the mainshock, a M w 5.7 aftershock occurred 9 km southeast of the community of Ocotillo at the northern end of the EMC rupture and aftershock zone (Hauksson et al, ; Kroll et al, , ; Ross et al, ). The aftershock sequence extended 6 km northwestward from the epicenter of the Ocotillo aftershock (Kroll et al, ). The main Ocotillo aftershock sequence continued for about 20 days following the event (Kroll et al, ).…”

“…The aftershock sequence extended 6 km northwestward from the epicenter of the Ocotillo aftershock (Kroll et al, ). The main Ocotillo aftershock sequence continued for about 20 days following the event (Kroll et al, ).…”

Seismicity and Stress Associated With a Fluid‐Driven Fracture: Estimating the Evolving Geometry

“…Though there are other friction laws that can provide a basis for fault rupture (Daub & Carlson, 2008), and hence seismic rate changes, rate‐ and state‐dependent friction has been used successfully in many applications and agrees with the results of careful experiments (Baumberger et al, 1999; Berthoud et al, 1999; Dieterich & Kilgore, 1994). For example, the theory has proven useful in the interpretation of stress transfer due to faulting and its impact on the seismicity following rupture on a fault (Harris & Simpson, 1998; Kroll et al, 2017; Stein, 1999). In this subsection we relate changes in stress and fluid pressure due to the changing fluid‐driven fracture to variations in the rate of microseismicity.…”

Inverse Migration of Seismicity Quiescence During the 2019 Ridgecrest Sequence

“…(2015) and Kroll et al. (2017), but are particularly challenging to observe for several reasons: (1) the computation of a decrease in seismicity rate requires smoothing, potentially over an extended period of time if the prior activity is too sparse (Marsan & Nalbant, 2005); (2) the reporting of earthquakes is not stationary after large mainshocks, resulting in many earthquakes being missed out that would normally be reported at more quiet times; (3) the decrease in activity can sometimes be dated to start prior to the mainshock (Marsan & Nalbant, 2005; Meng et al., 2013), raising doubts as to the exact role of the mainshock in causing this decrease.…”

“…This observational bias toward triggering has initially led some authors to doubt the existence of seismicity quiescences (Felzer & Brodsky, 2005; Mallman & Zoback, 2007), others arguing that they play an anecdotical role in the overall earthquake rate change budget (Marsan, 2003). However, observations of seismicity quiescences have since then accumulated, mostly for earthquake doublets (Daniel et al, 2006, 2008; Kroll et al., 2017; Ma et al., 2005; Marsan & Daniel, 2007; Marsan & Nalbant, 2005; Meng & Peng, 2014; Meng et al., 2013; Sevilgen et al., 2012; Toda & Stein 2002, 2003; Toda et al., 2012; Woessner et al., 2004; Wyss & Wiemer, 2000) or magma‐induced activity (Dieterich and Okubo, 1996; Dieterich et al., 2000; Green et al., 2015; Maccaferri et al., 2013), both types of systems being characterized by abundant seismicity prior to the appearance of the stress shadow.…”