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Intensity Lab
III

Max Est. MMI

M4.2 earthquake · shaking intensity by town 12 km ENE of Cloverdale, CA

Magnitude4.2
Depth2.9 km
Time 2026-01-08T08:00:21.950000Z UTC: 2026-01-08T08:00:21.950000Z
USGS ID nc75292441
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)
Cloverdale
CA 		760 346
Cobb
CA 		760 710
Kelseyville
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 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 -0.19 0.33 0.38
BSSA14 -0.26 0.36 0.45
CY14 -0.12 0.27 0.29
CB14 -0.20 0.34 0.39
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) 0.0354 Light(IV) 0.755 Weak(III)
Geyser Peak (NC.GGPC) 0.0329 Light(IV) 1.896 Light(IV)
Pine Mountain #1 (NC.GPM) 0.0211 Weak(III) 0.872 Weak(III)
Boggs Mountain (NC.GBG) 0.0077 Weak(III) 0.479 Weak(III)
Cloverdale #3 (NC.GCVB) 0.0053 Weak(II) 0.428 Weak(III)
Alexander Valley (NC.GAXB) 0.0046 Weak(II) 0.192 Weak(II)
Round Top Mountain (NC.GRT) 0.0024 Weak(II) 0.218 Weak(II)
Healdsburg Fire Station (NP.1744) 0.0024 Weak(II) 0.206 Weak(II)
Hopland Research and Extension Center, Hopland, CA, USA (BK.HOPS) 0.0022 Weak(II) 0.113 Weak(II)
Lake Bordeaux (NC.NLB) 0.0022 Weak(II) 0.079 Weak(II)
Skaggs, Las Lomas (BK.SKGS) 0.0020 Weak(II) 0.091 Weak(II)
Wildwood Ranch (NC.GWW) 0.0016 Weak(II) 0.093 Weak(II)
Thermalito Afterbay Dam (WR.THER) 0.0014 Weak(II) 0.014 Not felt(I)
Snow Mountain (NC.GSN) 0.0014 Weak(II) 0.079 Weak(II)
Cow Mountain (NC.GCWB) 0.0011 Not felt(I) 0.072 Weak(II)
Bradford Ranch, Boonville, CA (BK.BONV) 0.0010 Not felt(I) 0.053 Not felt(I)
Hamilton Opening (NC.GHO) 0.0009 Not felt(I) 0.059 Weak(II)
Weeks Lake (NC.NWS) 0.0009 Not felt(I) 0.040 Not felt(I)
Hirsch Winery property (BK.HRCH) 0.0008 Not felt(I) 0.042 Not felt(I)
Pepperwood Preserve (BK.PWOD) 0.0008 Not felt(I) 0.063 Weak(II)
St. Helena Fire Department (NP.1764) 0.0008 Not felt(I) 0.032 Not felt(I)
Austic Creek SRA (BK.AUSC) 0.0008 Not felt(I) 0.063 Weak(II)
Galbreath Preserve, Mendocino County, CA (BK.GALB) 0.0008 Not felt(I) 0.051 Not felt(I)
Mt.St.Helena South (NC.NHS) 0.0007 Not felt(I) 0.102 Weak(II)
Spanish Creek (BK.SPAN) 0.0006 Not felt(I) 0.029 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
Cloverdale
CA 		Weak(III)
Cobb
CA 		Weak(III)
Kelseyville
CA 		Weak(II)

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
Geyser Peak (NC.GGPC) Light(IV)
Pine Mountain #1 (NC.GPM) Weak(III)
Geysers (NC.GDXB) Weak(III)