Institute of Engineering Seismology and Earthquake Engineering and the U.S. Geological Survey2026-04-0117:11:32 UTCMap Version 2; Code Version 3.5Maphttp://earthquake.usgs.gov/eqcenter/shakemapShakeMap is designed as a rapid response tool to portray theextent and variation of ground shaking throughout the affectedregion immediately following significant earthquakes. Groundmotion and intensity maps are derived from peak ground motionamplitudes recorded on seismic sensors (accelerometers), withinterpolation based on both estimated amplitudes where data arelacking, and site amplification corrections. Color-codedinstrumental intensity maps are derived from empirical relationsbetween peak ground motions and Modified Mercalli intensity.This ShakeMap describes the event: auth2026gjth,S of Peloponnese - S. GreeceAs a rapid response tool, the ShakeMap ground motion values areused for emergency response, loss estimation, assessment of damageto the lifeline and utility networks, and for providing informationto the general public.2026-04-0117:11:32 UTCground conditionCompleteAs needed20.6200000000000023.6200000000000036.5640000000000034.11600000000000NoneShakeMappeak ground motionsshaking intensityinstrumental intensityearthquake damageAdvanced National Seismic Systems (ANSS)Institute of Engineering Seismology and Earthquake EngineeringNoneGlobalnonenoneShakeMap Working Group of ITSAKKiriaki KonstantinidouITmailing

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ThessalonikiN/AN/AGreece+30 2310 476081+30 2310 476085shakemaps@itsak.grhttp://shakemaps.itsak.gr/auth2026gjth/intensity.htmlInstrumental Intensity ShakeMap within a web page; all other ShakeMapmaps and products can be accessed from this site. Typicallythe image itself is 600x400 pixels and about 100k bytes in size.JPEGWald, D.J.Quitoriano, V.Heaton, T.H.Kanamori, H.Scrivner, C.W.Worden, C.B.1999Earthquake SpectraVol. 15, No. 3pp 537-556http://shakemaps.itsak.gr/about.html#referencesWald, D.J.Quitoriano, V.Heaton, T.H.Kanamori, H.1999Earthquake SpectraVol. 15, No. 3pp 557-564http://shakemaps.itsak.gr/about.html#referencesWald, D.J.Worden, C.B.Quitoriano, V.Pankow, K.2005U.S. Geological Survey [Open File Report][ZZZ-03][128 pp]http://pubs.usgs.gov/tm/2005/12A01/Slight variations in peak ground motions and spectral valuesmay depend on processing. Corrections or changes in stationand amplitude information are reflected by the authoritativeseismic network. In addition, changes in magnitude may resultin changes to estimated ground motions in areas with sparseseismic station coverage.Ground motion data are direct measurements only at the locationof seismic stations; all other data are interpolated (asdescribed in the citations). Seismic station coverage variesin density as well as instrumentation across the region inquestion. Uncertainty in the reported ground motions generallyincreases with distance from seismic stations, and in areas ofvery low station density may be largely the product of empiricalrelationships. Uncertainties in ground motions may also arisefrom inaccurate ground motion amplitudes from seismic stations,or inaccurate information regarding earthquake epicenter ormagnitude, as reported by the generating network.Included in this version are data available up to the time processed.Additional data (seismic stations) may be added at a later time.Shaking maps are prepared by contouring shaking informationinterpolated onto a square grid uniformly sampled at aspacing of 1 minute (about 1.6 km) throughout California. Ifthere were stations at each of the tens of thousands of gridpoints, then the creation of shaking maps would be relativelysimple. Of course stations are not available for all of thesegrid points, and in many cases grid points may be tens ofkilometers from the nearest reporting station. The overallmapping philosophy is to combine information from individualstations, geology (representing site amplification), and thedistance to the epicenter or causative fault to create thebest composite map. The procedure produces reasonable estimatesat grid points located far from available data, whilepreserving the detailed shaking information available forregions where there are stations nearby. Estimation of shaking over the regional extent for an earthquakein California is obtained by the spatial interpolation of themeasured ground motions with geologically based frequency andamplitude-dependent site corrections. We use the CaliforniaSite Condition Map (California Geological Survey, CGS) mapsof National Earthquake Hazard Reduction Program (NEHRP)classification site conditions as the basis for our sitecorrections. These site condition maps have coverage throughoutthe state at 1:250,000 scale (Wills et al., 2000). We use theamplification factors of Borcherdt et al. (1994). In addition,ShakeMap ground motions in regions of sparse station spacingare estimated using ground motion regression, initially froma point location at the epicenter. Later, as information aboutfault dimensions became available (in the form of aftershocks,source rupture models, and observed surface slip), the faultlocation and rupture dimensions are used as the basis forground motion estimation. First, peak ground motion parameters are recovered for eachstation and associated with a particular earthquake origin timeand epicenter. We then create a coarse, uniformly spaced gridof 30-km spaced "phantom" stations. Peak ground motions andspectral acceleration values are assigned to each coarse gridpoint using a ground motion attenuation relationship forrock sites given the magnitude of the earthquake and distanceto each grid point. In practice, we apply a static correctionto the amplitudes of the regression by using the network-determinedmagnitude, predicting the observed amplitudes, and correcting foran amplitude bias term between the predictions and the data. Site corrections are then used to interpolate from groundmotions recorded on a fairly sparse, non-uniformly spacednetwork of stations to maps showing spatially continuousfunctions (i.e., contours). Prior to interpolation, we reducethe ground motion amplitudes to a common reference, in thiscase bedrock motions. Peak ground motion amplitudes from theseismic stations are corrected to rock site conditions; andthe observations (corrected to rock) and the coarse phantomstations (computed for rock) are then interpolated to a finerock site grid (roughly 1.6-km spacing). We scale the peakacceleration (PGA) amplitude with the Borcherdt et al. (1994)short-period amplification factors while the peak groundvelocity (PGV) values are corrected with the mid-periodfactors. Response spectral values are scaled by the short-periodfactors at 0.3 sec, and by the mid-period response at 1.0 and3.0 seconds. The site correction procedure is applied so thatthe original data values are returned at each station; hence,the actual recorded motions are preserved in the process andthe final contours reflect the observations wherever they exist. Next, the interpolated rock grid is corrected at each pointfor local site amplification and instrumental intensity map isgenerated by relating the peak ground acceleration or velocityat each grid point to intensity as described by Wald et al. (1999).This fine grid is saved and exported to the file "grid.xyz". Acontinuous surface is also fit to the fine grid to producethe contour maps and GIS formatted maps.2026-04-0117:11:32 UTC0.024979591836730.02500000000000Decimal degreesWorld Geodetic System 1984WGS 846378137298.257mi.dbf (shapefile from "shape.zip" download file)Polygons of estimated instrumental intensityESRI Shapefile Technical DescriptionGRID_CODEEstimated instrumental intensity (double)Wald, et al., Relationship between Peak Ground Acceleration, PeakGround Velocity, and Modified Mercalli Intensity for Earthquakesin California, Earthquake Spectra, Vol. 15, No. 3, 1999, pp 557-564.0.010.0Intensity0.1VALUEEstimated instrumental intensity (double)Wald, et al., Relationship between Peak Ground Acceleration, PeakGround Velocity, and Modified Mercalli Intensity for Earthquakesin California, Earthquake Spectra, Vol. 15, No. 3, 1999, pp 557-564.0.010.0Intensity0.1pga.dbf (shapefile from "shape.zip" download file)Polygons of peak ground motion (acceleration)ESRI Shapefile Technical DescriptionGRID_CODEPeak ground motion (acceleration, as integer percent of g)self-evident-200.0200.0percent of g4VALUEPeak ground motion (acceleration, as fraction of g)self-evident-200.0200.0fraction of g0.04pgv.dbf (shapefile from "shape.zip" download file)Polygons of peak ground motion (velocity)ESRI Shapefile Technical DescriptionGRID_CODEPeak ground motion (velocity in cm/s, integer)self-evident-500.0500.0cm/s4VALUEPeak ground motion (velocity in cm/s, double)self-evident-500.0500.0cm/s4psa03.dbf (shapefile (from "shape.zip" download file)Polygons of spectral acceleration at 0.3 s period, 5% dampingESRI Shapefile Technical DescriptionGRID_CODESpectral acceleration at 0.3 s period, 5% damping (integer percent of g)self-evident-400.0400.0percent of g4VALUESpectral acceleration at 0.3 s period, 5% damping (fraction of g)self-evident-400.0400.0fraction of g0.04psa10.dbf (shapefile from "shape.zip" download file)Polygons of spectral acceleration at 1.0 s period, 5% dampingESRI Shapefile Technical DescriptionGRID_CODESpectral acceleration at 1.0 s period, 5% damping (integer percent of g)self-evident-400.0400.0percent of g4VALUESpectral acceleration at 1.0 s period, 5% damping (fraction of g)self-evident-400.0400.0fraction of g0.04psa30.dbf (shapefile from "shape.zip" download file)Polygons of spectral acceleration at 3.0 s period, 5% dampingESRI Shapefile Technical DescriptionGRID_CODESpectral acceleration at 3.0 s period, 5% damping (integer percent of g)self-evident234percent of g4VALUESpectral acceleration at 3.0 s period, 5% damping (fraction of g)self-evident-400.0400.0fraction of g0.04pga.dbf (shapefile from "hazus.zip" download file)Polygons of "mean" ground motion (acceleration), scaled from recorded peakvalues by 15% (empirical correction from peak to mean) to conform to HAZUS input requirements.ESRI Shapefile Technical DescriptionGRID_CODEMean ground motion (acceleration, as integer percent of g)self-evident-200.0200.0percent of g4VALUEMean ground motion (acceleration, as fraction of g)self-evident-200.0200.0fraction of g0.04pgv.dbf (shapefile (from "hazus.zip" download file)Polygons of "mean" ground motion (velocity), scaled from recorded peakvalues by 15% (empirical correction from peak to mean) to conform to HAZUS input requirements.ESRI Shapefile Technical DescriptionGRID_CODEMean ground motion (velocity in inches/sec, integer)self-evident-200.0200.0cm/s2VALUEMean ground motion (velocity in inches/s, double)self-evident-500.0500.0cm/s2.0psa03.dbf (shapefile from "hazus.zip" download file)Polygons of "mean" spectral acceleration at 0.3 s period, 5% damping, scaled fromrecorded peak values by 15% (empirical correction from peak to mean) to conform to HAZUS inputrequirements.ESRI Shapefile Technical DescriptionGRID_CODEMean Spectral acceleration at 0.3 s period, 5% damping (integer percent of g)self-evident-400.0400.0percent of g4VALUEMean spectral acceleration at 0.3 s period, 5% damping (fraction of g), scaledfrom recorded peak values by 15% (empirical correction from peak to mean) to conform to HAZUS inputrequirements.self-evident-400.0400.0fraction of g0.04psa10.dbf (shapefile from "hazus.zip" download file)Polygons of mean spectral acceleration at 1.0 s period, 5% damping, scaled fromrecorded peak values by 15% (empirical correction from peak to mean) to conform to HAZUS inputrequirements.ESRI Shapefile Technical DescriptionGRID_CODEMean spectral acceleration at 1.0 s period, 5% damping (integer percent of g)self-evident-400.0400.0percent of g4VALUEMean spectral acceleration at 1.0 s period, 5% damping (fraction of g), scaled fromrecorded peak values by 15% (empirical correction from peak to mean) to conform to HAZUS inputrequirements.self-evident-400.0400.0fraction of g0.04File 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:><name/CUSPID of event> <mag> <epicentral lat> <epicentral lon>><MMM DD YYYY> <HH:MM:SS timezone>><W bound> <S bound> <E bound> <N bound>>(Process time: <time>) <Location String> The first 'time' field is the time of the event.'Process time' is the time this file was last updated. For large or historic earthquakes the "Location String" willusually be the name of the earthquake, otherwise it will besomething of the form "12.1 mi. SSW of Carpinteria, CA" The remaining lines are of the form:><lon> <lat> <pga> <pgv> <mmi> <psa03> <psa10> <psa30> >pga = peak ground motion (acceleration, as percent of g)>pgv = peak ground motion (velocity in cm/s)>mmi = estimated instrumental intensity>psa03 = spectral acceleration at 0.3 s period, 5% damping (percent of g)>psa10 = spectral acceleration at 1.0 s period, 5% damping (percent of g)>psa30 = spectral acceleration at 3.0 s period, 5% damping (percent of g)http://shakemaps.itsak.gr/auth2026gjth/about_formats.html#xyzFile grid.xml Specifies the earthquake and ShakeMap parameters, and valuesof the peak amplitudes at the ShakeMap map grid nodes. File is XMLtext.http://shakemaps.itsak.gr/auth2026gjth/about_formats.html#xmlUnited States Geological Survey, Advanced National Seismic System (ANSS)David J WaldGeophysicistmailing address

P.O. Box 25046

LakewoodCO80225USA303-273-8441(303) 273-8600wald@usgs.govShakemap data for auth2026gjthSome USGS information accessed through this page may be preliminary innature and presented prior to final review and approval by theDirector of the USGS. This information is provided with theunderstanding that it is not guaranteed to be correct or complete, andconclusions drawn from such information are the sole responsibility ofthe user. These are automatic computer generated maps and have not necessarilybeen checked by human oversight, so they may contain errors. Further,the input data is raw and unchecked, and may contain errors. Contours can be misleading since data gaps may exist. Caution shouldbe used in deciding which features in the contour patterns arerequired by the data. Ground motions and intensities can vary greatlyover small distances, so these maps are only approximate; when mapsare enlarged beyond the limits of the original data in an effort toshow small areas, the maps are unreliable. These maps are preliminary in nature and will be updated as dataarrives from distributed sources. The estimated intensity map is derived from ground motions recorded byseismographs and represents Modified Mercalli Intensities (MMI's) thatare likely to have been associated with the ground motions. Unlikeconventional Modified Mercalli Intensities, the estimated intensitiesare not based on observations of the earthquake effects on people orstructures. Locations within the same intensity area will not necessarilyexperience the same level of damage since damage depends heavily onthe type of structure, the nature of the construction, and the detailsof the ground motion at that site. For this reason more or less damagethan described in the MMI scale may occur. Large earthquakes can generate very long-period ground motions thatcan cause damage at great distances from the epicenter; although theintensity estimated from the ground motions may be small, significanteffects to large structures (bridges, tall buildings, storage tanks)may be notable. The ground motion levels and descriptions associated with eachintensity value are based on recent damaging earthquakes. There may berevisions in these parameters as more data become available or fromfurther improvements in methodology.ESRI shapefileGround shaking intensity, acceleration, and velocity contoursunzip2 megabyteshttp://shakemaps.itsak.gr/auth2026gjth/download/shape.ziphttp://shakemaps.itsak.gr/auth2026gjth/download/hazus.zipText1.0Within lines, values are delimited by spaces. First line is a header containing <name/CUSPID of event> <mag><epicentral lat> <epicentral lon> <MMM DD YYYY> <HH:MM:SStimezone> <W bound> <S bound> <E bound> <N bound> (Process time:<time>) <Location String> The remaining lines contain <lon> <lat> <pga> <pgv> <mmi><psa03> <psa10> <psa30>Ground-shaking intensity and acceleration dataunzip0.5 megabyteshttp://shakemaps.itsak.gr/auth2026gjth/download/grid.xyz.zipnone2026-04-01U.S. Geological Survey, GEO-CR-GHTDavid J. WaldGeophysicistmailing

U.S. Geological SurveyP.O. Box 25046, Mail Stop 966

DenverCO80225-0046USA(303) 273-8441(303) 273-8600wald@usgs.govContent Standards for Digital Geospatial MetadataFGDC-STD-001-1998