Seismic and aseismic slip on the San Andreas Fault

Geophysical Research Letters, 1986

A "long" sequence of stick-slip cient) are approximately constant along the events generated along a laboratory fault, which fault. Stick-slip events generated in the model consists of eight spring-connected masses that are were found to show many similarities to earthelastically driven to slide on a frictional surface, has been examined to check whether the "large" events are predictable. The large events are found to recur at intervals of very different durations, although the elastic and frictional properties along the fault are quite uniform. The recurrence intervals are, however, approximately proportional to the displacements of the preceding quakes generated along a seismic fault; large events were found to generally occur at an approximately constant stress level and to have the maximum strain energy stored along the fault. masses may move twice in some cases, see Figure 3 in King [1975]), usually occur when most of the

Tectonic faults display a range of slip behaviors including continuous and episodic slip covering rates of more than 10 orders of magnitude (m/s). The physical control of such kinematic observations remains ambiguous. To gain insight into the slip behavior of brittle faults we performed laboratory stick-slip experiments using a rock analogue, granular material. We realized conditions under which our seismogenic fault analogue shows a variety of slip behaviors ranging from slow, quasi continuous creep to episodic slow slip to dynamic rupture controlled by a limited number of parameters. We explore a wide parameter space by varying loading rate from those corresponding to interseismic to postseismic rates and normal loads equivalent to hydrostatic to lithostatic conditions at seismogenic depth. The experiments demonstrate that significant interseismic creep and earthquakes may not be mutually exclusive phenomena and that creep signals vary systematically with the fault’s seismic poten...

J. Geophys. Res. Solid Earth, 2013

2011

We explore experimentally and theoretically how fault edges may affect earthquake and slip dynamics, as faults are intrinsically heterogeneous with common occurrences of jogs, edges and steps. In the presented experiments and accompanying theoretical model, shear loads are applied to the edge of one of two flat blocks in frictional contact that form a fault analog. We show that slip occurs via a sequence of rapid rupture events that initiate from the loading edge and are arrested after propagating a finite distance. This event succession extends the slip size, transfers the applied shear across the block, and causes progressively larger changes of the contact area along the contact surface. This sequence of events dynamically forms a hard asperity near the loading edge and largely reduces the contact area beyond. These sequences of rapid events culminate in slow slip events that precede a major, unarrested slip event along the entire contact surface. We show that the 1998 M5.0 Sendai and 1995 Off-Etorofu Earthquake sequences may correspond to this scenario. Our work demonstrates, qualitatively, how a simple deviation from uniform shear loading can significantly affect both earthquake nucleation processes and how fault complexity develops.

Bulletin of the Seismological Society of America, 1988

In addition to minor surface cracks in the region of the 8 July 1986 North Palm Springs earthquake, minor aseismic surficial rupture occurred along three segments of the San Andreas fault, 44 to 86 km southeast of the epicenter. Data from a creepmeter and a tiltmeter at one locality suggest that triggered slip occurred coseismically beneath the instruments but took 33 hr to propagate to the surface. That slippage occurred coseismically at depth favors mechanisms for triggered slip that involve dynamic or static strain changes rather than creep migrating from the source region. The distribution of slip along the San Andreas fault associated with the North Palm Springs earthquake differed significantly from that recorded after the moderate 1968 Borrego Mountain, California and 1979 Imperial Valley, California, earthquakes. During these earthquakes, triggered slip occurred along the San Andreas fault in the Durmid Hill area and in the Mecca Hills. Triggered slip associated with the Nor...

Geological Society of America Special Papers, 2011

Journal of Geophysical Research, 1999

We present the results of our mapping of a 5.6-km length of the central Emerson fault that ruptured during the 1992 Landers earthquake in the southwestern Mojave Desert, California. The right-lateral slip along this portion of the rupture varied from about 150 to 530 cm along the main rupture zone. In some locations a total of up to 110 cm of additional right-lateral slip occurred on secondary faults up to 1.7 km away from the main rupture zone. Other secondary faults carried up to several tens of centimeters of left-lateral or thrust displacement. The maximum net vertical displacement was 175 cm, east-side-up. The sense of vertical slip across the main fault zone varied along strike, but in most cases it was consistent with the sense of vertical slip in previous earthquakes, as indicated by the locations of areas of older, uplifted, and abandoned alluvial fan surfaces. Although variations in surficial slip have been reported along previous strike-slip ruptures, our closely spaced slip measurements allow a much more detailed study of slip variability than was possible previously. We document variations in slip as large as 1 rn or more over distances ranging from 1-2 km to a few tens of meters, suggesting that strains of the order of 10-1 may have occurred locally within the surficial sediments. The long-wavelength (kilometer-scale) variations in surficial slip may be influenced by fault geometry and perhaps by the thickness of unconsolidated sediments. The slip variations over shorter length scales (tens of meters) may be caused by variations in the proportion of the total shear that occurs on visible, brittle fractures versus that which occurs as distributed shear, warping or rotation. The variability of slip along the ruptures associated with the Landers earthquake calls for caution in interpreting geomorphic offsets along prehistoric fault ruptures.

Journal of Geophysical Research, 2010

Abstract[1] We present the first results from a dense network of 36 campaign and 46 continuous GPS stations located in the Eastern Transverse Ranges Province (ETR), a transition zone between the southernmost San Andreas fault (SSAF) and eastern California shear zone (ECSZ). We analyzed the campaign data together with available data from continuous GPS stations for the period 1994–2009. We used the GPS velocity estimates to constrain elastic block models to investigate fault-loading rates representing four hypotheses characterized by different fault-block geometries. Fault-block scenarios include blocks bounded by the east-striking left-lateral Pinto Mountain, Blue Cut, and Chiriaco faults of the ETR; blocks bounded by a right-lateral north-northwest striking structure (the “Landers-Mojave earthquake line”) that cuts obliquely across the ETR and mapped Mojave Desert faults; and combinations of these end-member hypotheses. Each model implies significantly different active fault geometries, block rotation rates, and slip rates for ETR and ECSZ structures. All models suggest that SSAF slip rate varies appreciably along strike, generally consistent with rates derived from tectonic geomorphology and paleoseismology, with a maximum of ∼23 mm/yr right-lateral along the southernmost Coachella Valley strand, decreasing systematically to <10 mm/yr right-lateral through the San Gorgonio Pass region. Slip rate estimates for the San Jacinto fault are ∼12 mm/yr for all models tested. All four models fit the data equally well in a statistical sense. Qualitative comparison among models and consideration of geologic slip rates and other independent data reveals strengths and weaknesses of each model.

2006

Transition zones are areas of mixed behavior that divide areas of velocity strengthening and velocity weakening frictional parameters. Their slip characteristics have implications for the underlying mechanism for interseismic creep, the relationship between aseismic slip and earthquakes, and the seismic potential of the transition zones. Two transition zones on the San Andreas fault in California, USA are included in this

Bulletin of the Seismological Society of America, 1994

We have determined a source rupture model for the 1992 Landers earthquake (Mw 7.2) compatible with multiple data sets, spanning a frequency range from zero to 0.5 Hz. Geodetic survey displacements, near-field and regional strong motions, broadband teleseismic waveforms, and surface offset measurements have been used explicitly to constrain both the spatial and temporal slip variations along the model fault surface. Our fault parameterization involves a variable-slip, multiple-segment, finite-fault model which treats the diverse data sets in a self-consistent manner, allowing them to be inverted both independently and in unison. The high-quality data available for the Landers earthquake provide an unprecedented opportunity for direct comparison of rupture models determined from independent data sets that sample both a wide frequency range and a diverse spatial station orientation with respect to the earthquake slip and radiation pattern. In all models, consistent features include the following: (1) similar overall dislocation patterns and amplitudes with seismic moments of 7 to 8 x 1026 dyne-cm (seismic potency of 2.3 to 2.7 km3);