Geology topics

Brian Chiou

Publications and source records attributed to Brian Chiou.

4 recordsLinked to original sources

USGS2025

Fault displacement model for surface principal rupture of strike-slip faults

The probability distribution model for principal displacement accommodated on the surface main trace is a critical input to the fault displacement hazard analysis. This article presents a new model for strike-slip ruptures in the moment magnitude ( M ) range of 6 to 8.3. The new model is the outcome of a multi-year research effort to update the widely used model developed by Petersen and others in 2011. Updates include the adoption of the Fault Displacement Hazard Initiative database and enhancements to rupture and displacement data preparation. Statistical formulation and estimation have also been updated substantially. A three-parameter modified normal distribution that we refer to as the negative Exponentially Modified Gaussian distribution is adopted to model the probability distribution of the natural logarithm of principal displacement. Formulation for the mean parameter of the modified normal includes a random earthquake term, a nonlinear scaling relation with M , and an ellipse function for along-main-trace variation. The aleatory variability of the updated model now depends on M as well as site’s along-main-trace position. These updates not only significantly improve the fit to the distribution of the observed displacements but also yield reasonable 95th percentile predictions for M > 7.5 events. Alternative models representing the estimation uncertainty of the M -scaling relation are also developed. These new models are compared to the previous model in terms of percentile predictions and the calculated hazard curves. The steeper hazard curves from the new models yield a lower exceedance rate than the normal-distribution based model developed previously by Petersen and others.

Earthquake Spectra↗

USGS2018

State transportation agencies partner to deploy and enhance ShakeCast

The California Department of Transportation (Caltrans) is organizing and leading a three-year Transportation Pooled Fund (TPF) project, Connecting the Dots: Implementing ShakeCast Across Multiple State Departments of Transportation for Rapid Post-Earthquake Response. Ten state Departments of Transportation (DOT)—CA, ID, MO, MS, OK, OR, SC, TX, UT, AND WA—have partnered and combined research funds to pursue implementation and advancement of the U.S. Geological Survey’s (USGS) ShakeCast system. ShakeCast is a software application that automatically retrieves ShakeMap shaking estimates and performs analyses using fragility functions for bridges, buildings, and other structures. The ShakeCast system identifies which facilities are most likely impacted by an earthquake and sends notifications to responders in the minutes after an earthquake. By focusing inspection efforts on the most damage-susceptible facilities in the severely shaken areas, ShakeCast can reduce response time and priorities for bridge inspections in the aftermath of a significant earthquake. The goal of the TPF project is to establish or enhance operational ShakeCast instances for all the partner DOTs, while advancing transportation-focused aspects of the software platform. DOTs are uniquely able to take advantage of the ShakeCast technology in that bridge fragilities can be readily derived from the National Bridge Inventory (NBI). DOTs also share the need for prioritized response strategies given their very large numbers of facilities—over wide areas—that have varying vulnerabilities, many of which could potentially be affected by earthquake shaking. The ten-state TPF project will also explore opportunities for DOT-specific ShakeCast software modifications, for example, for enhanced neighboring-state situational awareness and response coordination as well as for long-term maintenance and operations of their ShakeCast systems.

Conference Paper↗

USGS2015

Strike-parallel and strike-normal coordinate system around geometrically complicated rupture traces: use by NGA-West2 and further improvements

We present a two-dimensional system of generalized coordinates for use with geometrically complex fault ruptures that are neither straight nor continuous. The coordinates are a generalization of the conventional strike-normal and strike-parallel coordinates of a single straight fault. The presented conventions and formulations are applicable to a single curved trace, as well as multiple traces representing the rupture of branching faults or noncontiguous faults. An early application of our generalized system is in the second round of the Next Generation of Ground-Motion Attenuation Model project for the Western United States (NGA-West2), where they were used in the characterization of the hanging-wall effects. We further improve the NGA-West2 strike-parallel formulation for multiple rupture traces with a more intuitive definition of the nominal strike direction. We also derive an analytical expression for the gradient of the generalized strike-normal coordinate. The direction of this gradient may be used as the strike-normal direction in the study of polarization effects on ground motions.

Open-File Report↗

USGS2012

Directivity models produced for the Next Generation Attenuation West 2 (NGA-West 2) project

Five new directivity models are being developed for the NGA-West 2 project. All are based on the NGA-West 2 data base, which is considerably expanded from the original NGA-West data base, containing about 3,000 more records from earthquakes having finite-fault rupture models. All of the new directivity models have parameters based on fault dimension in km, not normalized fault dimension. This feature removes a peculiarity of previous models which made them inappropriate for modeling large magnitude events on long strike-slip faults. Two models are explicitly, and one is implicitly, 'narrowband' models, in which the effect of directivity does not monotonically increase with spectral period but instead peaks at a specific period that is a function of earthquake magnitude. These narrowband models' functional forms are capable of simulating directivity over a wider range of earthquake magnitude than previous models. The functional forms of the five models are presented.

Conference Paper↗