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III

Max Est. MMI

8 km ESE of Cloverdale, CA

Magnitude4.2
Depth5.5 km
Time 2026-07-29T02:40:06.730000Z UTC: 2026-07-29T02:40:06.730000Z
USGS ID nc75407577
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Ground Shaking Intensities — Interpolated ShakeMap MMI

3 sites
Location MMI Description
Cloverdale
CA
Weak(III)
Healdsburg
CA
Weak(III)
Cobb
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.

4 stations
Station MMI Description
Skaggs, Las Lomas (BK.SKGS) Light(IV)
Cloverdale #3 (NC.GCVB) Light(IV)
Geyser Peak (NC.GGPC) Light(IV)
Pine Mountain #1 (NC.GPM) Light(IV)

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
Healdsburg
CA
760 352
Cobb
CA
760 710

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 +0.31 0.53 0.62
BSSA14 +0.30 0.51 0.59
CY14 +0.30 0.52 0.60
CB14 +0.30 0.50 0.59
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)
Skaggs, Las Lomas (BK.SKGS) 0.0492 Light(IV) 1.889 Moderate(V)
Cloverdale #3 (NC.GCVB) 0.0480 Light(IV) 1.554 Moderate(V)
Geyser Peak (NC.GGPC) 0.0284 Light(IV) 1.252 Light(IV)
Geysers (NC.GDXB) 0.0207 Weak(III) 0.498 Weak(III)
Pine Mountain #1 (NC.GPM) 0.0184 Weak(III) 1.077 Light(IV)
Alexander Valley (NC.GAXB) 0.0131 Weak(II) 0.516 Weak(III)
Healdsburg Fire Station (NP.1744) 0.0076 Not felt(I) 0.365 Weak(III)
Hirsch Winery property (BK.HRCH) 0.0062 Not felt(I) 0.393 Weak(III)
Boggs Mountain (NC.GBG) 0.0044 Not felt(I) 0.156 Weak(II)
Austic Creek SRA (BK.AUSC) 0.0038 Not felt(I) 0.185 Weak(II)
Wildwood Ranch (NC.GWW) 0.0032 Not felt(I) 0.127 Weak(II)
Fort Ross (NC.NFRB) 0.0029 Not felt(I) 0.089 Weak(II)
Pepperwood Preserve (BK.PWOD) 0.0028 Not felt(I) 0.229 Weak(II)
Galbreath Preserve, Mendocino County, CA (BK.GALB) 0.0026 Not felt(I) 0.093 Weak(II)
Weeks Lake (NC.NWS) 0.0022 Not felt(I) 0.075 Weak(II)
Snow Mountain (NC.GSN) 0.0021 Not felt(I) 0.118 Weak(II)
Santa Rosa FS 1 (NP.1767) 0.0020 Not felt(I) 0.137 Weak(II)
Blucher Creek (NC.NBC) 0.0018 Not felt(I) 0.136 Weak(II)
Tomales (NC.NTOM) 0.0016 Not felt(I) 0.079 Weak(II)
Estero Americano (NC.NEA) 0.0016 Not felt(I) 0.069 Weak(II)
Forestville 2 (NC.NFVB) 0.0016 Not felt(I) 0.093 Weak(II)
The Novato Fire Protection District "Fire Station 1" (NP.1762) 0.0015 Not felt(I) 0.091 Weak(II)
Lake Bordeaux (NC.NLB) 0.0015 Not felt(I) 0.065 Weak(II)
Orr Springs (BK.ORRS) 0.0015 Not felt(I) 0.068 Weak(II)
Camp Tamarancho (NC.NCT) 0.0015 Not felt(I) 0.061 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.