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Intensity Lab
IV

Max Est. MMI

M4.1 earthquake · shaking intensity by town 7 km WSW of Holtville, CA

Magnitude4.1
Depth16.2 km
Time 2026-01-15T09:54:39.470000Z UTC: 2026-01-15T09:54:39.470000Z
USGS ID ci41158263
ShakeMap View USGS ↗

Engineering Ground Motion Parameters

GMPE predictions provide an independent check on the ShakeMap interpolated intensities above. ShakeMap relies on seismic station recordings; in areas with sparse station coverage — or for large teleseismic events and earthquakes outside dense West Coast networks — ShakeMap MMI can be inaccurate. A significant difference between ShakeMap and GMPE estimates is a signal that the ShakeMap result should be treated as preliminary. Also includes site Vs30 values and raw ground motion parameters (PGA/PGV).

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Est. Vs30 Values

Estimated shear-wave velocity in the upper 30 m used in GMPE calculations. Ref. column shows the 760 m/s rock-site reference for comparison.

Location Ref. (760 m/s) Est. Vs30 (m/s)
Holtville
CA 		760 218
Heber
CA 		760 228
El Centro
CA 		760 206

MMI vs Distance — Default Vs30 (760 m/s)

All methods using the 760 m/s rock-site reference. ShakeMap values are independent of Vs30.

MMI vs distance — default Vs30

MMI vs Distance — Est. Vs30

GMPEs use the Est. Vs30 values shown in the table above. ShakeMap values are independent of Vs30.

MMI vs distance — Est. Vs30

GMPE Residual — Observed − Predicted MMI

Signed residual at each seismic station. Positive values mean the GMPE underestimated shaking; negative values mean it overestimated. The dashed line at zero indicates perfect agreement.

GMPE residual plot

GMPE Predicted vs. Observed MMI at Seismic Stations

Each point is one seismic station. Points on the dashed 1:1 line indicate perfect agreement; above the line = GMPE underestimated shaking; below = overestimated.

GMPE predicted vs observed scatter

GMPE Performance — Station Observations

Statistics computed by comparing each GMPE's predicted MMI against ShakeMap observed MMI at seismic stations. Bias = mean(observed − predicted). Lower RMSE indicates better overall agreement with instrumental measurements.

GMPE Bias Sigma RMSE
ASK14 -0.05 0.31 0.32
BSSA14 +0.09 0.33 0.34
CY14 -0.06 0.32 0.32
CB14 -0.07 0.33 0.34
Bias > 0: GMPE underestimated shaking at stations. Bias < 0: GMPE overestimated shaking.

Peak Ground Motion — Seismic Station Observations

Recorded PGA and PGV at seismic stations, sorted by highest PGA. Top 25 stations shown. MMI (PGA) and MMI (PGV) are independent conversions via Worden et al. (2012) GMICE.

Station PGA (g) MMI (PGA) PGV (cm/s) MMI (PGV)
Bonds Corner, Omlin Residence (NP.5054) 0.0734 Moderate(V) 2.542 Light(IV)
Desert Research Extended Center (CI.DRE) 0.0656 Moderate(V) 1.836 Light(IV)
Schaffner Ranch (CI.SNR) 0.0355 Light(IV) 1.357 Light(IV)
CA:El Centro;ECA11 McCabe Sch (NP.5058) 0.0338 Light(IV) 1.531 Light(IV)
Fire Station (NP.5053) 0.0249 Weak(III) 1.245 Weak(III)
Imperial (CI.IMP) 0.0177 Weak(III) 0.909 Weak(III)
UABC Campus Mexicali (BC.UABX) 0.0177 Weak(III) 0.394 Weak(III)
Ocotillo Community Park (CI.OCP) 0.0176 Weak(III) 0.533 Weak(III)
El Centro (CI.ELO) 0.0155 Weak(III) 0.895 Weak(III)
San Luis Rio Colorado (BC.SLRCX) 0.0135 Weak(III) 0.293 Weak(III)
El Centro Array 1, Borchard Ranches (NP.5056) 0.0116 Weak(III) 0.631 Weak(III)
Coachella (CI.COA) 0.0102 Weak(III) 0.342 Weak(III)
Signal Mtn (CI.SGL) 0.0099 Weak(III) 0.300 Weak(III)
Yuha Desert (CI.YUH2) 0.0099 Weak(III) 0.128 Weak(II)
East Mesa (CI.EMS) 0.0098 Weak(III) 0.350 Weak(III)
Ejido Tlaxcala (BC.TL2X) 0.0096 Weak(III) 0.290 Weak(III)
Pescaderos la 14 (BC.PESCX) 0.0094 Weak(III) 0.256 Weak(II)
CERRO PRIETO (BC.CPX) 0.0094 Weak(III) 0.222 Weak(II)
American Girl Mine (CI.AGM) 0.0088 Weak(III) 0.241 Weak(II)
Carrizo (CI.CRR) 0.0081 Weak(III) 0.347 Weak(III)
Midway Well (NP.5272) 0.0072 Weak(III) 0.189 Weak(II)
Riito (BC.RITX) 0.0062 Weak(III) 0.218 Weak(II)
Elmore's Ranch (CI.ERR) 0.0061 Weak(III) 0.237 Weak(II)
Ejido Heriberto Jara (BC.JARAX) 0.0053 Weak(II) 0.233 Weak(II)
Salton City (CI.SAL) 0.0050 Weak(II) 0.189 Weak(II)
Source: USGS ShakeMap station recordings (view ShakeMap). PGA in g (fraction of gravitational acceleration); PGV in cm/s. The observed MMI shown on the map uses ShakeMap's reported instrumental intensity where available, or max(MMI from PGA, MMI from PGV) otherwise.

Ground Shaking Intensities — Interpolated ShakeMap MMI

3 sites
Location MMI Description
Holtville
CA 		Light(IV)
Heber
CA 		Weak(III)
El Centro
CA 		Weak(III)

Seismic Station Observed MMI

MMI values are derived directly from observed ground motion measurements at seismic stations and are not spatially interpolated.

5 stations
Station MMI Description
Bonds Corner, Omlin Residence (NP.5054) Light(IV)
Desert Research Extended Center (CI.DRE) Light(IV)
CA:El Centro;ECA11 McCabe Sch (NP.5058) Light(IV)
Schaffner Ranch (CI.SNR) Light(IV)
Fire Station (NP.5053) Light(IV)