Forecasting the evolution of seismicity in southern California: Animations built on earthquake stress transfer

Abstract

[1] We develop a forecast model to reproduce the distribution of main shocks, aftershocks and surrounding seismicity observed during 1986-2003 in a 300 Â 310 km area centered on the 1992 M = 7.3 Landers earthquake. To parse the catalog into frames with equal numbers of aftershocks, we animate seismicity in log time increments that lengthen after each main shock; this reveals aftershock zone migration, expansion, and densification. We implement a rate/state algorithm that incorporates the static stress transferred by each M ! 6 shock and then evolves. Coulomb stress changes amplify the background seismicity, so small stress changes produce large changes in seismicity rate in areas of high background seismicity. Similarly, seismicity rate declines in the stress shadows are evident only in areas with previously high seismicity rates. Thus a key constituent of the model is the background seismicity rate, which we smooth from 1981 to 1986 seismicity. The mean correlation coefficient between observed and predicted M ! 1.4 shocks (the minimum magnitude of completeness) is 0.52 for 1986-2003 and 0.63 for 1992-2003; a control standard aftershock model yields 0.54 and 0.52 for the same periods. Four M ! 6.0 shocks struck during the test period; three are located at sites where the expected seismicity rate falls above the 92 percentile, and one is located above the 75 percentile. The model thus reproduces much, but certainly not all, of the observed spatial and temporal seismicity, from which we infer that the decaying effect of stress transferred by successive main shocks influences seismicity for decades. Finally, we offer a M ! 5 earthquake forecast for 2005-2015, assigning probabilities to 324 10 Â 10 km cells. Motivation and Goals[2] There is growing evidence that large earthquakes can inhibit or promote failure on nearby faults for decades to centuries, and that the transfer of stress plays a governing role in this interaction [Harris, 1998;Stein, 1999;King and Cocco, 2000;Freed, 2005]. Some progress has also been achieved in explaining the time dependence of observed seismicity by Coulomb stress transfer in an elastic medium coupled with the concepts of Dieterich's [1994] rate and state friction [Stein et al., 1997;Parsons et al., 1999;Toda and Stein, 2003]. Competing and complementary concepts of dynamic stress triggering [Kilb, 2003;Gomberg et al., 2003], pore fluid diffusion [Peltzer et al., 1996], and viscoelastic stress transfer [Pollitz et al., 2004] have also been explored to explain aftershock and postseismic geodetic deformation, but here we will restrict ourselves to static stress changes coupled to rate/state friction.[3] Here we seek to explore how successive earthquakes redistribute stress, causing large, sudden seismicity rate changes that decay and are subsequently perturbed by other large shocks. To make the process more visible and accessible, we simulate the expected seismicity and compare it with the observations in several animations. To test the ability of the model to capture seismicity obser...

Shallow inland earthquakes in NE Japan possibly triggered by the 2011 off the Pacific coast of Tohoku Earthquake

“…We also assume the rake from each focal mechanism. We adopted the Coulomb 3.2 (Lin and Stein, 2004;Toda et al, 2005), assuming a frictional coefficient of 0.65. We calculate the static stress on each fault in a uniform and isotropic elastic half-space following Okada (1992).…”

“…In this study, we have investigated, in detail, hypocenter distributions of several events that occurred after the M w 9.0 earthquake in order to discriminate the fault plane from the auxiliary plane of the focal mechanism. We then calculated the Coulomb stress change (Lin and Stein, 2004;Toda et al, 2005) on each fault attributable to the 2011 M w 9.0 Tohoku Earthquake to explore whether or not they were likely triggered by the M w 9.0 event.…”

Investigation of Coulomb stress changes in south Tibet (central Himalayas) due to the 25th April 2015 M W 7.8 Nepal earthquake using a Coulomb stress transfer model

“…We make our calculations using Coulomb 3.3 (Toda et al 2005;Lin and Stein 2004) to estimate Coulomb stress along and across the rupturing fault in order to study the potential for future earthquakes on nearby faults or on a prescribed fault plane. The calculations are conducted in an elastic half-space with uniform isotropic elastic medium following the formulae of Okada (1992).…”

Ground deformation and fault modeling of the 2016 sequence (24 Aug. – 30 Oct.) in central Apennines (Central Italy)

“…Stress change distribution is calculated by the Coulomb v3.3 application (Toda et al, 2005) which resolves the shear and normal components of the stress change on a grid or on specified 'receiver' fault planes, in a homogeneous, elastic and isotropic half-space. According to Toda et al (2011), "source faults" are the faults that have slipped and "receiver faults" are planes with a specified strike, dip and rake, on which the stresses imparted by the source faults.…”

“…Our modelled seismic sources were used to calculate the cumulative ground deformation pattern after each main event of the sequence by applying the Okada (1992) dislocation solution formulae for a homogeneous, elastic and isotropic half-space, through the Coulomb v3.3 application (Toda et al, 2005). We will also compare our theoretical results with various published interferometric images, such as ALOS-2 (GSI, 2016) and Sentinel-1 (Copernicus Sentinel data, 2016; Marinkovic and Larsen, 2016).…”