Shallow slip deficit due to large strike-slip earthquakes in dynamic rupture simulations with elasto-plastic off-fault response (original) (raw)
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Bulletin of the Seismological Society of America, 2008
Coseismic slip is observed to increase with earthquake rupture length for lengths far beyond the length scale set by the seismogenic layer. The observation, when interpreted within the realm of static dislocation theory and the imposed limit that slip be confined to the seismogenic layer, implies that earthquake stress drop increases as a function of rupture length for large earthquakes and, hence, that large earthquakes differ from small earthquakes. Here, a three-dimensional elastodynamic model is applied to show that the observed increase in coseismic slip with rupture length may be satisfied while maintaining a constant stress drop across the entire spectrum of earthquake sizes when slip is allowed to penetrate below the seismogenic layer into an underlying zone characterized by velocity-strengthening behavior. Is this deep coseismic slip happening during large earthquakes? We point to a number of additional associated features of the model behavior that are potentially observable in the Earth. These include the predictions that a substantial fraction, on the order of onethird of the total coseismic moment, is due to slip below the seismogenic layer and that slip below the seismogenic layer should be characterized by long rise times and a dearth of high-frequency motion.
Journal of Geophysical Research, 1986
This paper develops an inversion technique for static surface displacements associated with shallow faulting and applies the method to geodetic observations of the Borah Peak, Idaho, earthquake (Ms=7.3) of October 28, 1983. This technique improves upon classical, uniform slip planar (USP) models by admitting earthquake faults which are curved and contain variable slip. By summing elemental point sources, employing a gradient strategy with positivity constraints, and combining both geodetic and surface scarp height data, we can now resolve fault orientation, dimension, shape, and slip distribution. Large formal misfits to the geodetic data and disagreements in observed surface scarp locations found with the best USP fault are eliminated in variable slip planar (VSP) models. The best VSP fault reaches to 18 km depth in the southeast but only to 3 km depth in the northwest. Surface slip and slip at depth are poorly correlated in the VSP model. In fact, toward the southeast, slip at depth extends 13 km beyond the terminus of the fault's surface expression. Three or four knots of concentrated slip are found in VSP models. These knots are 3-6 km in dimension and may represent the breaking of asperities. To test for listric-like behavior of the Borah Peak fault, we considered all possible variable slip listric (VSL) faults of parabolic shape. The best VSL model has a slight downward curvature; however, it does not fit the data significantly better than VSP models. The geodetic measurements do not support significant listric curvature at depths shallower than 20 km. Our techniques permit the calculation of sensitivity kernels for surface displacement. These functions explicitly reveal fault locations where a certain geodetic measurement is most sensitive. For faults like Borah Peak, a surface measurement at point r samples slip to a depth roughly equal to the distance from r to the fault trace. Consequently, near fault bench marks and surface scarp height measurements are very weak constraints on slip at depth. We feel that variable slip fault models will allow significant new interpretations to be drawn from the geodetic data pool concerning the physics of earthquakes and their potential hazard. us to address some important questions related to the characteristics of Basin and Range normal faults: (1) Is slip on 2. DATA the rupture surface uniform? (2) Do variations in surface scarp heights reflect variations in slip at depth? (3) Does• Three leveling surveys of the Borah Peak, Idaho, region the rupture surface flatten with depth as suggested in listric conducted by the National Geodetic Survey in 1933, 1948, fault models? and 1984 enable the static elevation changes associated with In modeling coseismic deformation, few workers have con-the earthquake of October 28, 1983, to be calculated. The sidered the possibilities of non-uniform slip over curved rup-northeastern elevations (points 1-23 in Figure 1) were meature surfaces. Typical analyses assume a rectangular fault sured in August 1948 with a second-order, single-run levon which the dislocation vector is everywhere constant [Stein eling. The southwestern portion of the 70-km-long route and Lisoswski, 1983; Mansinha and Staylie, 1971; Savage was carried out in 1933 using first-order, double-run stanand Hastie, 1966, 1969;Chinnery, 1961]. The restrictions dards which permitted comparatively smaller errors. The of uniform slip and planar rectangular faults, however, are only common points of the two routes are bench marks 22 probably unrealistic. In our work we have made substan-and 23. In spite of the disparity of standards required for tim improvement in the theory by removing these resttic-both levelings, the 1.58 mm discrepancy between the 1938 and 1948 measurements of the elevation difference between these two stations is actually smaller than the expected random error for a first-order survey. The July 1984 leveling, which reoccupied the 1933 and 1948 stations, was conducted Paper number 5B5671 to first-order, single-run standards over the central portion 0148-0227/86/005B-5671505.00 of the survey, but was double-run over 15 km at the ends 49O9 4910 WARD AND BARRIENTOS: FAULT SLIP FROM GEODETIC OBSERVATIONS 2O Borah Peak
Gradual Fault Weakening with Seismic Slip: Inferences from the Seismic Sequences of L
We estimate seismological fracture energies from two subsets of events selected from the seismic sequences of L' Aquila (2009), and Northridge (1994): 57 and 16 selected events, respectively, including the main shocks. Following ABERCROMBIE and RICE (Geophys J Int 162: 406-424, 2005), we postulate that fracture energy (G) represents the post-failure integral of the dynamic weakening curve, which is described by the evolution of shear traction as a function of slip. Following a direct-wave approach, we compute mainshock-/aftershock-source spectral ratios, and analyze them using the approach proposed by MALAG-NINI et al. (Pure Appl. Geophys., this issue, 2014) to infer corner frequencies and seismic moment. Our estimates of source parameters (including fracture energies) are based on best-fit gridsearches performed over empirical source spectral ratios. We quantify the source scaling of spectra from small and large earthquakes by using the MDAC formulation of WALTER and TAYLOR (A revised Magnitude and Distance Amplitude Correction (MDAC2) procedure for regional seismic discriminants, 2001). The source parameters presented in this paper must be considered as pointsource estimates representing averages calculated over specific ruptured portions of the fault area. In order to constrain the scaling of fracture energy with coseismic slip, we investigate two different slip-weakening functions to model the shear traction as a function of slip: (i) a power law, as suggested by ABERCROMBIE and RICE (Geophys J Int 162: 406-424, 2005), and (ii) an exponential decay. Our results show that the exponential decay of stress on the fault allows a good fit between measured and predicted fracture energies, both for the main events and for their aftershocks, regardless of the significant differences in the energy budgets between the large (main) and small earthquakes (aftershocks). Using the power-law slip-weakening function would lead us to a very different situation: in our two investigated sequences, if the aftershock scaling is extrapolated to events with large slips, a power law (a la Abercrombie and Rice) would predict unrealistically large stress drops for large, main earthquakes. We conclude that the exponential stress evolution law has the advantage of avoiding unrealistic stress drops and unbounded fracture energies at large slip values, while still describing the abrupt shear-stress degradation observed in high-velocity laboratory experiments (e.g., DI TORO et al., Fault lubrication during earthquakes, Nature 2011).
Tectonophysics, 2015
Earthquake recurrence models High-resolution topography lidar strike-slip faults slip accumulation pattern Understanding earthquake (EQ) recurrence relies on information about the timing and size of past EQ ruptures along a given fault. Knowledge of a fault's rupture history provides valuable information on its potential future behavior, enabling seismic hazard estimates and loss mitigation. Stratigraphic and geomorphic evidence of faulting is used to constrain the recurrence of surface rupturing EQs. Analysis of the latter data sets culminated during the mid-1980s in the formulation of now classical EQ recurrence models, now routinely used to assess seismic hazard. Within the last decade, Light Detection and Ranging (lidar) surveying technology and other high-resolution data sets became increasingly available to tectono-geomorphic studies, promising to contribute to better-informed models of EQ recurrence and slip-accumulation patterns. After reviewing motivation and background, we outline requirements to successfully reconstruct a fault's offset accumulation pattern from geomorphic evidence. We address sources of uncertainty affecting offset measurement and advocate approaches to minimize them. A number of recent studies focus on single-EQ slip distributions and along-fault slip accumulation patterns. We put them in context with paleoseismic studies along the respective faults by comparing coefficients of variation CV for EQ inter-event time and slip-per-event and find that a) single-event offsets vary over a wide range of length-scales and the sources for offset variability differ with length-scale, b) at fault-segment length-scales, single-event offsets are essentially constant, c) along-fault offset accumulation as resolved in the geomorphic record is dominated by essentially same-size, large offset increments, and d) there is generally no one-to-one correlation between the offset accumulation pattern constrained in the geomorphic record and EQ occurrence as identified in the stratigraphic record, revealing the higher resolution and preservation potential of the latter. While slip accumulation along a fault segment may be dominated by repetition of large, nearly constant offset increments, timing of surface-rupture is less regular. Tectonophysics j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / t e c t o Please cite this article as: Zielke, O., et al., Fault slip and earthquake recurrence along strike-slip faults -Contributions of high-resolution geomorphic data, Tectonophysics (2014), http://dx.
The Influence of Gravity on the Displacement Field Produced by Fault Slip
Geophysical Research Letters, 2017
We calculated surface displacements produced by a synthetic megathrust earthquake using two spherical, layered, elastic dislocation models which differ only in that one model accounts for the coupling between elasticity and gravity and the other does not. We show that including gravity perturbs the displacement field differently in the near‐, medium‐, and far‐fields. As a result, slip inversions based on an Earth model without gravity cannot simultaneously fit the near‐, medium‐ and far‐field displacements generated using a forward model including gravity. This suggests that the spatially systematic misfits between observations and dislocation predictions seen in the literature arise, at least in part, because these studies are based on models that neglect gravity. Although the magnitude of the far‐field displacements is small compared to those of the near‐field, our slip inversions show the most improvement when we both up‐weight the far‐field observations and use a physically cons...
Spatial and temporal distribution of slip for the 1992 Landers, California, earthquake
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);
Journal of Structural Geology, 2006
The spatial and temporal accumulation of slip from multiple earthquake cycles on active faults is poorly understood. Here, we describe a methodology that can determine the time period of observation necessary to reliably constrain fault behaviour, using a high-resolution longtimescale (the last 17 kyr) fault displacement dataset over the Rangitaiki Fault (Whakatane Graben, New Zealand). The fault linked at ca. 300 ka BP and analysis of time periods within the last 17 kyr gives insight into steady-state behaviour for time intervals as short as ca. 2 kyr. The maximum displacement rate observed on the Rangitaiki Fault is 3.6G1.1 mm yr K1 measured over 17 kyr. Displacement profiles of the last 9 ka of fault movement are similar to profiles showing the last 300 ka of fault movement. In contrast, profiles determined for short time intervals (2-3 kyr) are highly irregular and show points of zero displacement on the larger segments. This indicates temporal and spatial variability in incremental displacement associated with surface-rupturing slip events. There is spatial variability in slip rates along fault segments, with minima at locations of fault interaction or where fault linkage has occurred in the past. This evidence suggests that some earthquakes appear to have been confined to specific segments, whereas larger composite ruptures have involved the entire fault. The short-term variability in fault behaviour suggests that fault activity rates inferred from geodetic surveys or surface ruptures from a single earthquake may not adequately represent the longer-term activity nor reflect its future behaviour. Different magnitude events may occur along the same fault segment, with asperities preventing whole segment rupture for smaller magnitude events. q