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Intensity Lab
IV

Max Est. MMI

M4.2 earthquake · shaking intensity by town 8 km ESE of Cloverdale, CA

Magnitude4.2
Depth5.9 km
Time 2026-07-29T02:40:06.730000Z UTC: 2026-07-29T02:40:06.730000Z
USGS ID nc75407577
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
Healdsburg
CA 		760 352

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 -0.07 0.32 0.32
BSSA14 -0.09 0.31 0.32
CY14 -0.01 0.30 0.30
CB14 -0.02 0.31 0.31
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 Light(IV)
Cloverdale #3 (NC.GCVB) 0.0480 Light(IV) 1.554 Light(IV)
Geyser Peak (NC.GGPC) 0.0284 Light(IV) 1.252 Weak(III)
Geysers (NC.GDXB) 0.0207 Weak(III) 0.498 Weak(III)
Pine Mountain #1 (NC.GPM) 0.0184 Weak(III) 1.077 Weak(III)
Alexander Valley (NC.GAXB) 0.0131 Weak(III) 0.516 Weak(III)
Healdsburg Fire Station (NP.1744) 0.0076 Weak(III) 0.365 Weak(III)
Hirsch Winery property (BK.HRCH) 0.0062 Weak(III) 0.393 Weak(III)
Boggs Mountain (NC.GBG) 0.0044 Weak(II) 0.156 Weak(II)
Austic Creek SRA (BK.AUSC) 0.0038 Weak(II) 0.185 Weak(II)
Wildwood Ranch (NC.GWW) 0.0032 Weak(II) 0.127 Weak(II)
Fort Ross (NC.NFRB) 0.0029 Weak(II) 0.089 Weak(II)
Pepperwood Preserve (BK.PWOD) 0.0028 Weak(II) 0.229 Weak(II)
Galbreath Preserve, Mendocino County, CA (BK.GALB) 0.0026 Weak(II) 0.093 Weak(II)
Weeks Lake (NC.NWS) 0.0022 Weak(II) 0.075 Weak(II)
Snow Mountain (NC.GSN) 0.0021 Weak(II) 0.118 Weak(II)
Santa Rosa FS 1 (NP.1767) 0.0020 Weak(II) 0.137 Weak(II)
Blucher Creek (NC.NBC) 0.0018 Weak(II) 0.136 Weak(II)
Tomales (NC.NTOM) 0.0016 Weak(II) 0.079 Weak(II)
Estero Americano (NC.NEA) 0.0016 Weak(II) 0.069 Weak(II)
Forestville 2 (NC.NFVB) 0.0016 Weak(II) 0.093 Weak(II)
The Novato Fire Protection District "Fire Station 1" (NP.1762) 0.0015 Weak(II) 0.091 Weak(II)
Lake Bordeaux (NC.NLB) 0.0015 Weak(II) 0.065 Weak(II)
Orr Springs (BK.ORRS) 0.0015 Weak(II) 0.068 Weak(II)
Camp Tamarancho (NC.NCT) 0.0015 Weak(II) 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.

Ground Shaking Intensities — Interpolated ShakeMap MMI

3 sites
Location MMI Description
Cloverdale
CA 		Light(IV)
Cobb
CA 		Weak(II)
Healdsburg
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)