Intensity Lab
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III

Max Est. MMI

6 km WNW of The Geysers, CA

Magnitude3.6
Depth3.7 km
Time 2026-03-08T10:31:07.640000Z UTC: 2026-03-08T10:31:07.640000Z
USGS ID nc75324182
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Ground Shaking Intensities — Interpolated ShakeMap MMI

3 sites
Location MMI
Cobb
CA 		III
Cloverdale
CA 		II
Middletown
CA 		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
Geysers (NC.GDXB) IV
Geyser Peak (NC.GGPC) IV
Alexander Valley (NC.GAXB) III

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)
Cobb
CA 		760 710
Cloverdale
CA 		760 346
Middletown
CA 		760 294

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 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 +0.08 0.36 0.37
BSSA14 +0.08 0.33 0.34
CY14 +0.08 0.33 0.34
CB14 +0.07 0.29 0.30
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)
Geysers (NC.GDXB) 0.0815 V 1.641 V
Geyser Peak (NC.GGPC) 0.0183 III 0.829 IV
Boggs Mountain (NC.GBG) 0.0148 III 0.316 III
Pine Mountain #1 (NC.GPM) 0.0081 II 0.289 III
Lake Bordeaux (NC.NLB) 0.0044 I 0.117 II
Alexander Valley (NC.GAXB) 0.0042 I 0.145 II
Weeks Lake (NC.NWS) 0.0023 I 0.077 II
Round Top Mountain (NC.GRT) 0.0010 I 0.064 II
CA:St. Helena;FS 17 (NP.1764) 0.0009 I 0.027 II
Mt.St.Helena South (NC.NHS) 0.0007 I 0.046 II
Cloverdale #3 (NC.GCVB) 0.0006 I 0.038 II
Healdsburg Fire Station (NP.1744) 0.0006 I 0.042 II
Skaggs, Las Lomas (BK.SKGS) 0.0006 I 0.024 I
Lloyd Lowery (NC.NLL) 0.0005 I 0.018 I
Smittle Creek (NC.NSC) 0.0005 I 0.024 I
Oakville Experimental Vineyard, Oakville (BK.OAKV) 0.0004 I 0.022 I
Santa Rosa FS 7 (NP.1835) 0.0004 I 0.014 I
Berryessa Peak (NC.NBPB) 0.0004 I 0.019 I
Pepperwood Preserve (BK.PWOD) 0.0004 I 0.021 I
Austic Creek SRA (BK.AUSC) 0.0004 I 0.020 I
Adams Ridge, Knoxville, Napa County (BK.ADAM) 0.0003 I 0.012 I
Ca: San Francisco; Fire Sta 40 (NP.1792) 0.0003 I 0.004 I
Rominger Bros.; near Winters (BK.ROMB) 0.0002 I 0.017 I
Moore Creek Park, Napa County (BK.MORK) 0.0002 I 0.006 I
Santa Rosa FS 1 (NP.1767) 0.0002 I 0.012 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.