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Intensity Lab
III

Max Est. MMI

M3.6 earthquake · shaking intensity by town 7 km S of Brawley, CA

Magnitude3.6
Depth9.4 km
Time 2026-07-23T07:31:48.570000Z UTC: 2026-07-23T07:31:48.570000Z
USGS ID ci40659802
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)
Brawley
CA 		760 227
Imperial
CA 		760 227
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 0.27 0.28
BSSA14 -0.01 0.25 0.24
CY14 -0.02 0.26 0.26
CB14 +0.00 0.26 0.26
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)
Imperial (CI.IMP) 0.0608 Moderate(V) 1.470 Light(IV)
El Centro Array 5, James Rd (NP.952) 0.0447 Light(IV) 1.500 Light(IV)
El Centro Array 3, Pine School (NP.5057) 0.0246 Weak(III) 0.523 Weak(III)
Airport Hangar (NP.5060) 0.0206 Weak(III) 0.399 Weak(III)
Desert Research Extended Center (CI.DRE) 0.0093 Weak(III) 0.566 Weak(III)
Cook Ranch 2 (CI.COK2) 0.0071 Weak(III) 0.151 Weak(II)
El Centro Array 9, Imperial Irrigation District Su (NP.117) 0.0066 Weak(III) 0.228 Weak(II)
Schaffner Ranch (CI.SNR) 0.0055 Weak(II) 0.158 Weak(II)
Bonds Corner, Omlin Residence (NP.5054) 0.0042 Weak(II) 0.161 Weak(II)
El Centro Array 11, McCabe School (NP.5058) 0.0041 Weak(II) 0.171 Weak(II)
El Centro (CI.ELO) 0.0041 Weak(II) 0.123 Weak(II)
El Centro Array 1, Borchard Ranches (NP.5056) 0.0036 Weak(II) 0.147 Weak(II)
Ocotillo Community Park (CI.OCP) 0.0032 Weak(II) 0.118 Weak(II)
Fire Station (NP.5053) 0.0025 Weak(II) 0.121 Weak(II)
Calipatria 2 (CI.CLI2) 0.0022 Weak(II) 0.092 Weak(II)
Elmore's Ranch (CI.ERR) 0.0020 Weak(II) 0.080 Weak(II)
Ejido Yucatan (BC.YUC2X) 0.0018 Weak(II) 0.063 Weak(II)
Coachella (CI.COA) 0.0018 Weak(II) 0.051 Not felt(I)
CERRO PRIETO (BC.CPX) 0.0016 Weak(II) 0.048 Not felt(I)
Fire Station (NP.5491) 0.0015 Weak(II) 0.055 Not felt(I)
Ruthven (CI.RUN) 0.0015 Weak(II) 0.042 Not felt(I)
Campo Elementary School (CI.CPO) 0.0015 Weak(II) 0.025 Not felt(I)
Yuha Desert (CI.YUH2) 0.0015 Weak(II) 0.014 Not felt(I)
UABC Campus Mexicali (BC.UABX) 0.0014 Weak(II) 0.064 Weak(II)
Salton Sea Wildlife (SSW) (NP.5062) 0.0011 Not felt(I) 0.046 Not felt(I)
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
Brawley
CA 		Weak(III)
Imperial
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.

3 stations
Station MMI Description
Imperial (CI.IMP) Light(IV)
El Centro Array 5, James Rd (NP.952) Light(IV)
Airport Hangar (NP.5060) Weak(III)