The magnitude 7.3 Landers earthquake of 28 June 1992 triggered a remarkably sudden and widespread increase in earthquake activity across much of the western United States. The triggered earthquakes, which occurred at distances up to 1250 kilometers (17 source dimensions) from the Landers mainshock, were confined to areas of persistent seismicity and strike-slip to normal faulting. Many of the triggered areas also are sites of geothermal and recent volcanic activity. Static stress changes calculated for elastic models of the earthquake appear to be too small to have caused the triggering. The most promising explanations involve nonlinear interactions between large dynamic strains accompanying seismic waves from the mainshock and crustal fluids (perhaps including crustal magma).

A-1. Plot of probability of surface rupture relative to magnitude A-2. Plot of depth to top of surface rupture relative to magnitude for earthquakes in Next Generation Attenuation database B-1. Plot of multisegment fault as defined in 1996 and 2002 maps B-2. Plot of multisegment fault as defined in 2008 maps D-1. Diagram of a virtual dipping fault D-2. Plots showing effect of including hanging-wall term on median ground motion D-3. Plot showing the increase in Rjb for vertical faults F-1. Ground motions for two sites in the Central and Eastern United States without cluster model F-2. Ground motions for two sites in the Central and Eastern United States with cluster model G-1. Map of fault sources in the Intermountain West G-2. Slip-rate changes for Intermountain West faults H-1. Map of fault sources in the Pacific Northwest J-1. Plot showing increase in characteristic rate due to magnitude rounding J-2. Plot showing uncertainty in assigned slip rate for selected faults in Utah Appendix Tables: A-1. Depth to top of rupture E-1. Sampling interval details for non-California faults, truncated Gutenberg-Richter distribution G-1. Updated Intermountain West fault parameters G-2. Updated fault names for Intermountain West faults G-3. Intermountain West fault parameters by State H-1. Pacific Northwest fault parameters by State I-1. Rupture-model data for California Type-A faults I-2. List of significant changes to California Type-B faults I-3. Parameters for California Type-B faults I-4. Parameters for California Connected-B faults

The national seismic hazard maps for the conterminous United States have been updated to account for new methods, models, and data that have been obtained since the 2008 maps were released (Petersen and others, 2008). The input models are improved from those implemented in 2008 by using new ground motion models that have incorporated about twice as many earthquake strong ground shaking data and by incorporating many additional scientific studies that indicate broader ranges of earthquake source and ground motion models. These time-independent maps are shown for 2-percent and 10-percent probability of exceedance in 50 years for peak horizontal ground acceleration as well as 5-hertz and 1-hertz spectral accelerations with 5-percent damping on a uniform firm rock site condition (760 meters per second shear wave velocity in the upper 30 m, V S30). In this report, the 2014 updated maps are compared with the 2008 version of the maps and indicate changes of plus or minus 20 percent over wide areas, with larger changes locally, caused by the modifications to the seismic source and ground motion inputs.

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The Conditional Spectrum (CS) is a target spectrum (with conditional mean and conditional standard deviation) that links seismic hazard information with ground motion selection for nonlinear dynamic analysis. Probabilistic seismic hazard analysis (PSHA) estimates the ground motion hazard by incorporating the aleatory uncertainties in all earthquake scenarios and resulting ground motions as well as the epistemic uncertainties in ground motion prediction models (GMPMs) and seismic source models. Typical CS calculations to date are produced for a single earthquake scenario using a single GMPM, but more precise use requires consideration of at least multiple causal earthquakes and multiple GMPMs that are often considered in a PSHA computation. This paper presents the mathematics underlying these more precise CS calculations. Despite requiring more effort to compute than approximate calculations using a single causal earthquake and GMPM, the proposed approach produces an exact output that has a theoretical basis. To demonstrate the results of this approach and compare the exact and approximate calculations, several example calculations are performed for real sites in the western U.S. (WUS). The results also provide some insights regarding the circumstances under which approximate results are likely to closely match more exact results. To facilitate these more precise calculations for real applications, the exact CS calculations can now be performed for real sites in the U.S. using new deaggregation features in the U.S. Geological Survey hazard mapping tools. Details regarding this implementation are discussed in this paper.