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Wedescribe aweighted-average approach for incorporating varioustypes of data (observed peak ground motions and intensities and estimates from ground- motion prediction equations) into theShakeMap ground motion and intensity mapping framework.ThisapproachrepresentsafundamentalrevisionofourexistingShakeMap methodology. In addition, the increased availability of near-real-time macroseismic intensitydata,thedevelopmentofnewrelationshipsbetweenintensityandpeakground motions, and new relationships to directly predict intensity from earthquake source information have facilitated the inclusion of intensity measurements directly into ShakeMap computations. Our approach allows for the combination of (1) direct observations (ground-motion measurements or reported intensities), (2) observations converted from intensity to ground motion (or vice versa), and (3) estimated ground motionsandintensities frompredictionequationsornumerical models.Critically,each oftheaforementioneddatatypesmustincludeanestimateofitsuncertainties,including those caused by scaling the influence of observations to surrounding grid points and those associated with estimates given an unknown fault geometry. The ShakeMap ground-motion and intensity estimates are an uncertainty-weighted combination of these various data and estimates. A natural by-product of this interpolation process is an estimate of total uncertainty at each point on the map, which can be vital for comprehensive inventory loss calculations. We perform a number of tests to validate this new methodology and find that it produces a substantial improvement in the accuracy of ground-motion predictions over empirical prediction equations alone.

A simple procedure is presented to resolve locations of regional earthquakes with poor quality of recorded phases and/or a very large gap in seismograph recording geometry. In solving earthquake locations, we use a modified G matrix containing S - P time intervals and P - P and S - S time differences between stations and a forward method. Unlike the regular G matrix, which consists of three spatial parameters ( x, y, z ) and one timing parameter ( t ), the modified G matrix contains only two spatial parameters ( x, y ) and a fixed depth ( z ). The origin time parameter is eliminated by using only relative time intervals. In the new G matrix, two base equations instead of one are used. The S - P time intervals constrain epicentral distance, and P - P and S - S time differences constrain the distribution of azimuth. In searching for epicenters, we first divide the modified G matrix based on individual time intervals then map deviations between theoretical and observed time intervals into logic space using the fuzzy logic technique. Resolutions of earthquake locations are enhanced in the logic space by applying logic operations among individual G matrices. Final locations are derived by searching for a center of gravity in the output matrix. Test results indicate that this method effectively avoids the local minimum problem encountered by generalized inverse methods when data are recorded by small aperture arrays from earthquakes outside the arrays or when large errors occur in phase readings.

For 35 years, strong reflected phases from the sill-like, mid-crustal Socorro magma body (SMB) have been observed on microearthquake seismograms recorded in the central Rio Grande rift, New Mexico. In 1979, the lateral extent of the SMB was estimated at 1700 km2 by mapping reflection points for 220 observed SzS arrivals. We have remapped the magma body using 697 PzP, 2169 SzP, and 2589 SzS reflections observed on seismograms recorded between 1975 and 1995 by New Mexico Tech seismic networks. These data indicate that the SMB covers an area greater than 3400 km2. By comparing the distribution of observed reflection points with the distribution of all possible reflection points, limits can be set for the northern and southern boundaries of the SMB. The ∼80 km north-south extent of the SMB falls just inside a ∼100-km north-south range of enhanced seismicity near Socorro. This area, the Socorro seismic anomaly (SSA), covers ∼5000 km2 and has the same elliptical shape as the outline of the SMB based on observed reflection points. The close spatial relation between the SSA and the mid-crustal magma body along their northern and southern boundaries suggests that the observed seismicity can be used to place limits on the eastern and western boundaries of the magma body. Using the distribution of earthquakes within the SSA over the last 34 years, the maximum east-west extent of the SMB is Our data indicates that the upper surface of the magma body displays no regional dip. Considering timing errors, maximum possible relief on the magma body surface is ±0.50 km.