Kasey W. Schultz

Simulating Gravity Changes in Topologically Realistic Driven Earthquake Fault Systems: First Results

Currently, GPS and InSAR measurements are used to monitor deformation produced by slip on earthquake faults. It has been suggested that another method to accomplish many of the same objectives would be through satellite-based gravity measurements. The Gravity Recovery and Climate Experiment (GRACE) mission has shown that it is possible to make detailed gravity measurements from space for climate dynamics and other purposes. To build the groundwork for a more advanced satellite-based gravity survey, we must estimate the level of accuracy needed for precise estimation of fault slip in earthquakes. We turn to numerical simulations of earthquake fault systems and use these to estimate gravity changes. The current generation of Virtual California (VC) simulates faults of any orientation, dip, and rake. In this work, we discuss these computations and the implications they have for accuracies needed for a dedicated gravity monitoring mission. Preliminary results are in agreement with previous results calculated from an older and simpler version of VC. Computed gravity changes are in the range of tens of μGal over distances up to a few hundred kilometers, near the detection threshold for GRACE.

Spatial Evaluation and Verification of Earthquake Simulators

In this paper, we address the problem of verifying earthquake simulators with observed data. Earthquake simulators are a class of computational simulations which attempt to mirror the topological complexity of fault systems on which earthquakes occur. In addition, the physics of friction and elastic interactions between fault elements are included in these simulations. Simulation parameters are adjusted so that natural earthquake sequences are matched in their scaling properties. Physically based earthquake simulators can generate many thousands of years of simulated seismicity, allowing for a robust capture of the statistical properties of large, damaging earthquakes that have long recurrence time scales. Verification of simulations against current observed earthquake seismicity is necessary, and following past simulator and forecast model verification methods, we approach the challenges in spatial forecast verification to simulators; namely, that simulator outputs are confined to the modeled faults, while observed earthquake epicenters often occur off of known faults. We present two methods for addressing this discrepancy: a simplistic approach whereby observed earthquakes are shifted to the nearest fault element and a smoothing method based on the power laws of the epidemic-type aftershock (ETAS) model, which distributes the seismicity of each simulated earthquake over the entire test region at a decaying rate with epicentral distance. To test these methods, a receiver operating characteristic plot was produced by comparing the rate maps to observed

Recurrence Time Distributions of Large Earthquakes in Eastern Iran

m>6.0

Stacking catalogue sources in WMAP data

m>6.0 earthquakes in California since 1980. We found that the nearest-neighbor mapping produced poor forecasts, while the ETAS power-law method produced rate maps that agreed reasonably well with observations.

Forecasting Earthquakes with the Virtual Quake Simulator: Regional and Fault-Partitioned Catalogs

With the ever increasing number of geodetic monitoring satellites, it is vital to have a variety of geophysical simulations produce synthetic datasets. Furthermore, just as hurricane forecasts are derived from the consensus among multiple atmospheric models, earthquake forecasts cannot be derived from a single comprehensive model. Here we present the functionality of Virtual Quake (formerly known as Virtual California), a numerical simulator that can generate sample co-seismic deformations, gravity changes, and InSAR interferograms in addition to producing probabilities for earthquake scenarios.Virtual Quake is now hosted by the Computational Infrastructure for Geodynamics. It is available for download and comes with a user manual. The manual includes a description of the simulator physics, instructions for generating fault models from scratch, and a guide to deploying the simulator in a parallel computing environment. http://geodynamics.org/cig/software/vq/.

The Virtual Quake earthquake simulator: a simulation-based forecast of the El Mayor-Cucapah region and evidence of predictability in simulated earthquake sequences

The eastern part of the Iranian plateau is characterized by large and infrequent earthquakes with recurrence intervals of more than several hundred years. Given that previous observations and paleoseismological studies are insufficient for forecasting large earthquakes, we have developed a physics‐based synthetic seismicity model for the fault system in eastern Iran using the Virtual Quake simulator. The model is independent of the seismic catalogs, however, it is tuned to match available earthquakes records. We show that the modeled seismicity rates and empirical frequency–magnitude distributions are consistent within the uncertainty of the empirical relations. Furthermore, our synthetic catalog agrees with previous paleoseismological investigations. From the resulting catalog, we can obtain the statistical distributions of recurrence times and waiting times for large earthquakes in the region as a whole and for the individual faults. In agreement with previous earthquake simulator studies, we find that the Poisson (time‐independent) distribution best describes the recurrence times of large earthquakes in the region as a whole. Large earthquakes on the individual faults show quasi‐periodic behavior, and for most faults can be well represented by the Weibull distribution. We present the corresponding time‐dependent conditional probabilities for large earthquakes throughout the region and for a few selected individual faults. Long‐term simulations indicate that waiting times for large earthquakes on specific faults are strongly dependent on the fault system configuration. Faults confined by other active faults, or consisting of several segments, host large earthquakes with more distributed recurrence times. Moreover, the obtained long‐term synthetic seismic catalog shows that fault interactions clearly have a major effect on occurrence of large earthquakes, and hence should be taken into account for seismic‐hazard assessment.

The Virtual Quake Earthquake Simulator: Earthquake Probability Statistics for the El Mayor-Cucapah Region and Evidence of Predictability in Simulated Earthquake Sequences

Utilizing earthquake source parameter scaling relations, we formulate an extensible slip weakening friction law for quasi-static earthquake simulations. This algorithm is based on the method used to generate fault strengths for a recent earthquake simulator comparison study of the California fault system. Here we focus on the application of this algorithm in the Virtual Quake earthquake simulator. As a case study we probe the effects of the friction law’s parameters on simulated earthquake rates for the UCERF3 California fault model, and present the resulting conditional probabilities for California earthquake scenarios. The new friction model significantly extends the moment magnitude range over which simulated earthquake rates match observed rates in California, as well as substantially improving the agreement between simulated and observed scaling relations for mean slip and total rupture area.

Virtual Quake and Tsunami Squares: Scenario Earthquake and Tsunami Simulations for a Pacific Rim GNSS Tsunami Early Warning System

We stack WMAP 7-year temperature data around extragalactic point sources, showing that the proles are consistent with WMAP’s beam models, in disagreement with the ndings of Sawangwit & Shanks (2010a). These results require that the source sample’s selection is not biased by CMB uctuations. We compare proles from sources in the standard WMAP catalog, the WMAP catalog selected from a CMB-free combination of data, and the NVSS catalog, and quantify the agreement with ts to simple parametric beam models. We estimate the biases in source proles due to alignments with positive CMB uctuations, nding them roughly consistent with those biases found with the WMAP standard catalog. Addressing those biases, we nd source spectral indices signicantly steeper than those used by WMAP, with strong evidence for spectral steepening above 61 GHz. Such changes modify the power spectrum correction required for unresolved point sources, and tend to weaken somewhat the evidence for deviation from a Harrison-Zel’dovich primordial spectrum, but more analysis is required. Finally, we discuss implications for current CMB experiments.