[1] We analyzed 315 dynamic strike-slip rupture models computed up to 5.0 Hz to get a quantitative understanding of the correlation and amplitude distributions of parameters describing the earthquake source, such as slip and rupture velocity. To account for the epistemic uncertainty of the problem, we constructed a database of dynamic ruptures computed by ourselves and other authors. This database contains ruptures computed using different models of initial stress, peak stress, and critical slip-weakening distance. Using the set of computed ruptures, we constructed probability density functions (pdfs) for the amplitude distributions of the source parameters and for the correlation between the source parameters. We tried to extract parameter pairs that showed a small variability in the spatial correlation given the large epistemic uncertainty in the input. We only analyzed the areas on the fault with subshear propagation speed. The principal findings are as follows: (1) Final slip amplitude does not show correlation with the local rupture velocity. (2) Final slip amplitude correlates well with risetime. (3) Rupture velocity correlates well with peak slip rate and the duration of the impulsive part of the slip rate function. (4) The pdf of rupture velocity, risetime, and peak slip rate depends on the distance from the nucleation zone. (5) Fracture energy is not the single controlling factor for the rupture velocity; the slope of the linear slip-weakening curve has a significant effect on the rupture velocity. (6) The crack length (length that is slipping at a given time) decreases with the distance from the nucleation zone.

SUMMARY Teleseismic receiver functions (RFs) represent an estimate of the site‐response to incoming seismic energy. This technique has long been a staple of the global earthquake community, as RFs are sensitive to impedance contrasts associated with major discontinuities in the crust and upper mantle. However, there is substantial debate in the community concerning the lateral and vertical resolution limits possible using these methods due to limitations resulting from ambient noise and non‐uniform spatial sampling of finite‐frequency wave kernels. Here, we take advantage of data from the LaBarge Passive Seismic Experiment to examine these questions in more detail. We find (1) that RFs can provide a robust image of the near‐surface (<5 km) structure; (2) that vertical resolution may exceed 500 m and (3) that our results compare favourably to nearby wells. These results indicate that RF analysis can provide high‐resolution images of the shallow crust, which has potential value for hydrocarbon exploration.

The effects of near-surface soil stratigraphy on the amplitude and frequency content of ground motion are accounted for in most modern U.S. seismic design codes for building structures as a function of the soil conditions prevailing in the area of interest. Nonetheless, currently employed site-classification criteria do not adequately describe the nonlinearity susceptibility of soil formations, which prohibits the development of standardized procedures for the computationally efficient integration of nonlinear ground response analyses in broadband ground-motion simulations. In turn, the lack of a unified methodology for nonlinear site-response analyses affects both the prediction accuracy of site-specific ground-motion intensity measures and the evaluation of site-amplification factors when broadband simulations are used for the development of hybrid attenuation relations. In this article, we introduce a set of criteria for quantification of the nonlinearity susceptibility of soil profiles based on the site conditions and incident ground-motion characteristics, and we implement them to identify the least complex ground response prediction methodology required for the simulation of nonlinear site effects at three sites in the Los Angeles basin. The criteria are developed on the basis of a comprehensive nonlinear site-response modeling uncertainty analysis, which includes both detailed soil profile descriptions and statistical adequacy of ground-motion time histories. Approximate and incremental nonlinear models are implemented, and the limited site-response observations are initially compared to the ensemble site-response estimates. A suite of synthetic ground motions for rupture scenarios of weak, medium, and large magnitude events (M 3:5-7:5) is next generated, parametric studies are conducted for each fixed magnitude scenario by varying the source-to-site distance, and the variability introduced in ground-motion predictions is quantified for each nonlinear site-response methodology. A frequency index is developed to describe the frequency content of incident ground motion relative to the resonant frequencies of the soil profile, and this index is used in conjunction with the rock-outcrop acceleration peak amplitude (PGA RO ) to identify the site conditions and ground-motion characteristics where incremental nonlinear analyses should be employed in lieu of approximate methodologies. We show that the proposed intensity-frequency representation of ground motion may be implemented to describe the nonlinearity susceptibility of soil formations in broadband simulations by accounting both for the magnitude-distance-orientation characteristics of seismic motion and the profile stiffness characteristics. The synthetic ground-motion predictions are next used for the development of site-amplification factors for the alternative site-response methodologies, and the results are compared to published site factors of attenuation relations. For the site conditions investigated, currently established amplification fac...

No abstract

Empirical data suggest that peak ground acceleration (PGA) and peak ground velocity (PGV) saturate as a function of magnitude for large magnitude ruptures close to the fault. Because data are sparse in the near-source region of large magnitude events, we have explored this question by simulating large magnitude strike-slip earthquakes. We use kinematic simulations to generate ground motion for a strike-slip fault that has a large aspect ratio (length/width). We consider both homogeneous or heterogeneous rupture models. We find that close to the fault along strike profiles of PGV and PGA increase to a maximum at a certain epicentral distance and then decrease to an asymptotic level beyond this distance. Critical factors for predicting ground motion are the position of an observer along strike, the depth of the hypocenter below the top of the fault, and the ratio of rupture velocity to shear-wave velocity. To understand the cause of the amplitude variation of along strike profiles of PGV and PGA, we use the isochrone method and the concept of the critical point to investigate how the geometry and kinematic parameters interact to produce the computed ground motion. We construct a predictor based on the critical point that does well in predicting the position of the maximum of PGV and PGA for stations close to the fault. For heterogeneous rupture models we find that the behavior is more complex though the general observation that along strike profiles of PGV and PGA increase to a maximum and then decrease still holds. This has implications for empirical attenuation relationships that essentially average the ground motion for all stations along strike with the same distance to the fault.