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Record Search Query: [Personnel: Last_Name='EARTHQUAKE HAZARDS PROGRAM OFFICE']

Earthquake Directivity Model
Entry ID: USGS_isodirect

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Abstract: Isodirect1 is a MATLAB-language function for modeling seismic directivity at user-selected sites around a user-defined fault. Isodirect1.m implements the Spudich and Chiou (Earthquake Spectra, 2008) directivity model. The results of isodirect1.m should be combined with the ground motion predictions of a non-directive predictive model like any of the four NGA models. Input to isodirect1.m consists ... View entire text
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Description: This package contains MATLAB-language 'main program' isodirect.m, two scripts that call isodirect1.m to calculate predicted directivity for five test cases, and numeric and plotted output from those test cases.

Description: Directivity in NGA Earthquake Ground Motions: Analysis Using Isochrone Theory:

We present correction factors that may be applied to the ground motion prediction relations of Abrahamson and Silva, Boore and Atkinson, Campbell and Bozorgnia, and Chiou and Youngs (all in this volume) to model the azimuthally varying distribution of the GMRotI50 component of ground motion (commonly called “directivity”) around earthquakes. Our correction factors may be used for planar or nonplanar faults having any dip or slip rake (faulting mechanism). Our correction factors predict directivity-induced variations of spectral acceleration that are roughly half of the strike-slip variations predicted by Somerville et al. (1997), and use of our factors reduces record-to-record sigma by about 2–20% at 5 sec or greater period.
Service Citation
Title: Earthquake Directivity Model
Provider: U.S. Geological Survey
Service Keywords

ISO Topic Category
Access Constraints None
Ancillary Keywords
Predictive Modeling
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Service Provider
DOI/USGS/GD/EHP > Earthquake Hazards Program, Geological Division, U.S. Geological Survey, U.S. Department of the Interior Supplemental Info
Service Organization URL:

Service Provider Personnel
Contact Address:
12201 Sunrise Valley Drive, MS 905
City: Reston
Province or State: VA
Postal Code: 20192
Country: USA
Distribution Media
Distribution_Media: Online
Distribution_Size: 15 MB
Fees: No fees
Contact Address:
12201 Sunrise Valley Drive, MS 905
City: Reston
Province or State: VA
Postal Code: 20192
Country: USA
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Creation and Review Dates
SERF Creation Date: 2012-02-06
SERF Last Revision Date: 2012-02-07
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