Coseismic fault slip associated with the 1992 M_w 6.1 Joshua Tree, California, earthquake: Implications for the Joshua Tree‐Landers earthquake sequence

Abstract

Coseismic surface deformation associated with the Mw 6.1, April 23, 1992, Joshua Tree earthquake is well represented by estimates of geodetic monument displacements at 20 locations independently derived from Global Positioning System and trilateration measurements. The rms signal to noise ratio for these inferred displacements is 1.8 with near-fault displacement estimates exceeding 40 mm. In order to determine the long-wavelength distribution of slip over the plane of rupture, a Tikhonov regularization operator is applied to these estimates which minimizes stress variability subject to purely right-lateral slip and zero surface slip constraints. The resulting slip distribution yields a geodetic moment estimate of 1.7x10 is N m with corresponding maximum slip around 0.8 m and compares well with independent and complementary information including seismic moment and source time function estimates and main shock and aftershock locations. From empirical Green's function analyses, a rupture duration of 5 s is obtained which implies a rupture radius of 6-8 km. Most of the inferred slip lies to the north of the hypocenter, consistent with northward rupture propagation. Stress drop estimates are in the range of 2-4 MPa. In addition, predicted Coulomb stress increases correlate remarkably well with the distribution of aftershock hypocenters; most of the aftershocks occur in areas for which the mainshock rupture produced stress increases larger than about 0.1 MPa. In contrast, predicted stress changes are near zero at the hypocenter of the Mw 7.3, June 28, 1992, Landers earthquake which nucleated about 20 km beyond the northernmost edge of the Joshua Tree rupture. Based on aftershock migrations and the predicted static stress field, we speculate that redistribution of Joshua Tree-induced stress perturbations played a role in the spatio-temporal development of the earthquake sequence culminating in the Landers event. Introduction The Mw 6.1, April 23, 1992, Joshua Tree, California, earthquake resulted from right-lateral rupture along a previously unmapped north trending late Quaternary fault located about 20 km south of the Pinto Mountain fault and about 10 km northeast of the MissionCreek branch of the San Andreas fault system (Figures 1 and 2). This and other subparallel late Quaternary faults, identified following the earthquake, offset an older northwest trending system [Rymer, 1992]. Seismicity here is characterized by frequent earthquake swarms suggesting that faults in the area are immature [Hauksson et al., 1993]. It is also the location of a sequence of moderate earthquakes occurring between 1940 and 1948 [Richter et al., 1958; Sykes and Seebet, 1985] which included the 1940 M5 5.3 Covington Flat, 1947 M5 5.4 Morongo Valley, and 1948 M5 6.5 Desert Hot Springs earthquakes. The Covington Flat earthquake likely involved rupture along one of these north trending faults, possibly the same fault ruptured during the Joshua Tree earthquake. These north trending faults lie in what is known as the Eastern California Shear Zon...

Fault interaction and stress triggering of twentieth century earthquakes in Mongolia

“…It is found that the spatial distribution of aftershocks is well explained in terms of a Coulomb failure criterion [ King et al , 1994] that involves a linear combination of the shear and normal tractions from a primary earthquake evaluated on a secondary fault plane. (Counterexamples, though relatively few, may be noted [ Astiz et al , 2000; Bennett et al , 1995; Dodge et al , 1995; Du and Aydin , 1993]. ) The time dependence of aftershock occurrence is less well understood, with chief candidate processes being rate‐ and state‐dependent friction [ Gross and Kisslinger , 1997; Gross and Bürgmann , 1998; Price and Bürgmann , 2002], dissipation of pore fluid gradients [ Jaume and Sykes , 1992], and viscoelastic relaxation of the lower crust and mantle [ Deng et al , 1999].…”

A search for evidence of secondary static stress triggering during the 1992 Mw7.3 Landers, California, earthquake sequence

“…We calculate stresses from the same three earthquakes (the "main shock" group) and contrast these with those of the smaller but more numerous and clustered "aftershocks" (the "aftershock" group). For the main shocks Joshua Tree, Landers, and Big Bear, we calculate stresses from slip models published by Bennett [1995], Wald and Heaton [1994], and Jones and Hough [1995], respectively (available from http://equake-rc.info/srcmod/). For the smaller events for which no finite-fault models are available we use the focal mechanism catalog of Yang et al [2012] (in the following referred to as YHS catalog), which contains n = 6613 earthquakes with M ≥ 2 within 95 days of the M w 6.4 Big Bear earthquake (the last of the three large events) within the study region of Woessner et al [2011] (117.5…”

Geometry of crustal faults: Identification from seismicity and implications for slip and stress transfer models

“…Using such small search volumes, the method does not find seismicity that elucidates the fault zone structure of the Joshua Tree fault. Alternatively, one could choose very large search volumes (see single search volume for the Joshua Tree segment or roughly 25 km) and one would arrive at planar models similar to those used in prior studies [e.g., Bennett et al , ]. We limit the size of the search volumes to 10 km along strike, or nearly the depth‐extent (12 km) of the seismogenic portions of the faults in the region.…”

“…There a further dense cloud of seismicity is found. The relative sparsity of the seismicity in the center of the Joshua Tree fault is attributed to main rupture location with a radius of roughly 5–6 km [ Bennett et al , ].…”