Identification_Information: Citation: Citation_Information: Originator: CISN/cgs and the U.S. Geological Survey Publication_Date: 2023-03-18 Publication_Time: 17:19:33 UTC Title: Advanced National Seismic System (ANSS), ShakeMap, CISN/cgs Region, Maps of ground shaking and intensity for event 40186575, 13 km (8.125 mi) SSW of Bombay Beach, CA Edition: Map Version 1; Code Version 3.5 Geospatial_Data_Presentation_Form: Map Online_Linkage: http://earthquake.usgs.gov/eqcenter/shakemap Description: Abstract: ShakeMap is designed as a rapid response tool to portray the extent and variation of ground shaking throughout the affected region immediately following significant earthquakes. Ground motion and intensity maps are derived from peak ground motion amplitudes recorded on seismic sensors (accelerometers), with interpolation based on both estimated amplitudes where data are lacking, and site amplification corrections. Color-coded instrumental intensity maps are derived from empirical relations between peak ground motions and Modified Mercalli intensity. This ShakeMap describes the event: 40186575, 13 km (8.125 mi) SSW of Bombay Beach, CA Purpose: As a rapid response tool, the ShakeMap ground motion values are used for emergency response, loss estimation, assessment of damage to the lifeline and utility networks, and for providing information to the general public. Time_Period_of_Content: Currentness_Reference: ground condition Time_Period_Information: Single_Date/Time: Calendar_Date: 2023-03-18 Time_of_Day: 17:19:33 UTC Status: Progress: Complete Maintenance_and_Update_Frequency: As needed Spatial_Domain: Bounding_Coordinates: West_Bounding_Coordinate: -117.04600000000001 East_Bounding_Coordinate: -114.54600000000001 North_Bounding_Coordinate: 34.08053400000000 South_Bounding_Coordinate: 32.41386600000000 Keywords: Theme: Theme_Keyword_Thesaurus: None Theme_Keyword: ShakeMap Theme_Keyword: peak ground motions Theme_Keyword: shaking intensity Theme_Keyword: instrumental intensity Theme_Keyword: earthquake damage Theme_Keyword: Advanced National Seismic Systems (ANSS) Theme_Keyword: CISN/cgs Place: Place_Keyword_Thesaurus: None Place_Keyword: CISN/cgs Access_Constraints: none Use_Constraints: none Point_of_Contact: Contact_Information: Contact_Organization_Primary: Contact_Organization: ShakeMap Working Group Contact_Person: David J. Wald Contact_Position: Geophysicist Contact_Address: Address_Type: mailing Address: N/A City: N/A State_or_Province: N/A Postal_Code: N/A Country: USA Contact_Voice_Telephone: N/A Contact_Facsimile_Telephone: N/A Contact_Electronic_Mail_Address: N/A Browse_Graphic: Browse_Graphic_File_Name: http://earthquake.usgs.gov/shakemap/global/shake/40186575/intensity.html Browse_Graphic_File_Description: Instrumental Intensity ShakeMap within a web page; all other ShakeMap maps and products can be accessed from this site. Typically the image itself is 600x400 pixels and about 100k bytes in size. Browse_Graphic_File_Type: JPEG Cross_Reference: Citation_Information: Originator: Wald, D.J. Originator: Quitoriano, V. Originator: Heaton, T.H. Originator: Kanamori, H. Originator: Scrivner, C.W. Originator: Worden, C.B. Title: TriNet "ShakeMaps": rapid generation of instrumental ground motion and intensity maps for earthquakes in Southern California Publication_Date: 1999 Series_Information: Series_Name: Earthquake Spectra Issue_Identification: Vol. 15, No. 3 Other_Citation_Details: pp 537-556 Online_Linkage: http://earthquake.usgs.gov/shakemap/global/shake/about.html#references Cross_Reference: Citation_Information: Originator: Wald, D.J. Originator: Quitoriano, V. Originator: Heaton, T.H. Originator: Kanamori, H. Title: Relationship between Peak Ground Acceleration, Peak Ground Velocity, and Modified Mercalli Intensity for Earthquakes in California Publication_Date: 1999 Series_Information: Series_Name: Earthquake Spectra Issue_Identification: Vol. 15, No. 3 Other_Citation_Details: pp 557-564 Online_Linkage: http://earthquake.usgs.gov/shakemap/global/shake/about.html#references Cross_Reference: Citation_Information: Originator: Wald, D.J. Originator: Worden, C.B. Originator: Quitoriano, V. Originator: Pankow, K. Title: ShakeMap Manual: Users Guide, Technical Manual, and Software Guide, USGS Techniques and Methods 12-A1 Publication_Date: 2005 Series_Information: Series_Name: U.S. Geological Survey [Open File Report] Issue_Identification: [ZZZ-03] Other_Citation_Details: [128 pp] Online_Linkage: http://pubs.usgs.gov/tm/2005/12A01/ Data_Quality_Information: Attribute_Accuracy: Attribute_Accuracy_Report: Slight variations in peak ground motions and spectral values may depend on processing. Corrections or changes in station and amplitude information are reflected by the authoritative seismic network. In addition, changes in magnitude may result in changes to estimated ground motions in areas with sparse seismic station coverage. Completeness_Report: Included in this version are data available up to the time processed. Additional data (seismic stations) may be added at a later time. Logical_Consistency_Report: Ground motion data are direct measurements only at the location of seismic stations; all other data are interpolated (as described in the citations). Seismic station coverage varies in density as well as instrumentation across the region in question. Uncertainty in the reported ground motions generally increases with distance from seismic stations, and in areas of very low station density may be largely the product of empirical relationships. Uncertainties in ground motions may also arise from inaccurate ground motion amplitudes from seismic stations, or inaccurate information regarding earthquake epicenter or magnitude, as reported by the generating network. Lineage: Process_Step: Process_Description: Shaking maps are prepared by contouring shaking information interpolated onto a square grid uniformly sampled at a spacing of 1 minute (about 1.6 km) throughout California. If there were stations at each of the tens of thousands of grid points, then the creation of shaking maps would be relatively simple. Of course stations are not available for all of these grid points, and in many cases grid points may be tens of kilometers from the nearest reporting station. The overall mapping philosophy is to combine information from individual stations, geology (representing site amplification), and the distance to the epicenter or causative fault to create the best composite map. The procedure produces reasonable estimates at grid points located far from available data, while preserving the detailed shaking information available for regions where there are stations nearby. Estimation of shaking over the regional extent for an earthquake in California is obtained by the spatial interpolation of the measured ground motions with geologically based frequency and amplitude-dependent site corrections. We use the California Site Condition Map (California Geological Survey, CGS) maps of National Earthquake Hazard Reduction Program (NEHRP) classification site conditions as the basis for our site corrections. These site condition maps have coverage throughout the state at 1:250,000 scale (Wills et al., 2000). We use the amplification factors of Borcherdt et al. (1994). In addition, ShakeMap ground motions in regions of sparse station spacing are estimated using ground motion regression, initially from a point location at the epicenter. Later, as information about fault dimensions became available (in the form of aftershocks, source rupture models, and observed surface slip), the fault location and rupture dimensions are used as the basis for ground motion estimation. First, peak ground motion parameters are recovered for each station and associated with a particular earthquake origin time and epicenter. We then create a coarse, uniformly spaced grid of 30-km spaced "phantom" stations. Peak ground motions and spectral acceleration values are assigned to each coarse grid point using a ground motion attenuation relationship for rock sites given the magnitude of the earthquake and distance to each grid point. In practice, we apply a static correction to the amplitudes of the regression by using the network-determined magnitude, predicting the observed amplitudes, and correcting for an amplitude bias term between the predictions and the data. Site corrections are then used to interpolate from ground motions recorded on a fairly sparse, non-uniformly spaced network of stations to maps showing spatially continuous functions (i.e., contours). Prior to interpolation, we reduce the ground motion amplitudes to a common reference, in this case bedrock motions. Peak ground motion amplitudes from the seismic stations are corrected to rock site conditions; and the observations (corrected to rock) and the coarse phantom stations (computed for rock) are then interpolated to a fine rock site grid (roughly 1.6-km spacing). We scale the peak acceleration (PGA) amplitude with the Borcherdt et al. (1994) short-period amplification factors while the peak ground velocity (PGV) values are corrected with the mid-period factors. Response spectral values are scaled by the short-period factors at 0.3 sec, and by the mid-period response at 1.0 and 3.0 seconds. The site correction procedure is applied so that the original data values are returned at each station; hence, the actual recorded motions are preserved in the process and the final contours reflect the observations wherever they exist. Next, the interpolated rock grid is corrected at each point for local site amplification and instrumental intensity map is generated by relating the peak ground acceleration or velocity at each grid point to intensity as described by Wald et al. (1999). This fine grid is saved and exported to the file "grid.xyz". A continuous surface is also fit to the fine grid to produce the contour maps and GIS formatted maps. Process_Date: 2023-03-18 Process_Time: 17:19:33 UTC Spatial_Reference_Information: Horizontal_Coordinate_System_Definition: Geographic: Latitude_Resolution: 0.00555556000000 Longitude_Resolution: 0.00555555555556 Geographic_Coordinate_Units: Decimal degrees Geodetic_Model: Horizontal_Datum_Name: World Geodetic System 1984 Ellipsoid_Name: WGS 84 Semi-major_Axis: 6378137 Denominator_of_Flattening_Ratio: 298.257 Entity_and_Attribute_Information: Overview_Description: Entity_and_Attribute_Overview: File grid.xyz Values of the peak amplitudes at the ShakeMap map grid nodes. File is ASCII text in the following format: First line is a header, space-delimited, with all of the following: > > > >(Process time: