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III

Max Est. MMI

10 km W of Boonville, CA

Magnitude3.7
Depth4.0 km
Time 2026-09-26T03:42:49.570000Z UTC: 2026-09-26T03:42:49.570000Z
USGS ID nc75442207
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)
Boonville
CA
760 371
Ukiah
CA
760 312
Talmage
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 +0.14 0.56 0.57
BSSA14 +0.13 0.54 0.55
CY14 +0.13 0.54 0.55
CB14 +0.13 0.52 0.53
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)
Forest View Rd, Manchester, CA (NC.G007) 0.0246 Weak(III) 0.606 Weak(III)
Bradford Property, Boonville, CA (BK.BONV) 0.0146 Weak(II) 0.547 Weak(III)
Beacon Light (NC.GBL) 0.0070 Not felt(I) 0.255 Weak(II)
Orr Springs (BK.ORRS) 0.0030 Not felt(I) 0.154 Weak(II)
Clifton Court South - FF (WR.CLFS) 0.0006 Not felt(I) 0.012 Not felt(I)
Barra Winery, Redwood Valley CA (BK.BARR) 0.0003 Not felt(I) 0.015 Not felt(I)
CA: Belmont; APEEL Station 6 (NP.1003) 0.0002 Not felt(I) 0.005 Not felt(I)
CA: Larkspur; Ferry Terminal (NP.1814) 0.0002 Not felt(I) 0.011 Not felt(I)
Ca: Oakland; Fire Station 23 (P03) (NP.1855) 0.0002 Not felt(I) 0.010 Not felt(I)
Taylor Ranch; Willits, CA USA (BK.DCMP) 0.0002 Not felt(I) 0.009 Not felt(I)
Cloverdale (NC.GCVB) 0.0002 Not felt(I) 0.011 Not felt(I)
CA: Healdsburg; Fire Station (NP.1744) 0.0002 Not felt(I) 0.013 Not felt(I)
CA:Oakland;Fire Station 13 (NP.1857) 0.0001 Not felt(I) 0.006 Not felt(I)
Ca: Oakland; FD Fire Training Center (P1 (NP.1861) 0.0001 Not felt(I) 0.012 Not felt(I)
Ca: Oakland; Fire Station 20 (P10) (NP.1859) 0.0001 Not felt(I) 0.008 Not felt(I)
Hales Grove, Mendocino, CA (BK.HALS) 0.0001 Not felt(I) 0.009 Not felt(I)
Berkeley Country Club (NP.1737B) 0.0001 Not felt(I) 0.006 Not felt(I)
Ca: Mt View; Fire Sta 3 (NP.1775) 0.0001 Not felt(I) 0.003 Not felt(I)
CA: Santa Rosa Firestation 7 (NP.1835) 0.0001 Not felt(I) 0.005 Not felt(I)
Ca: San Francisco; Fire Sta 40 (NP.1792) 0.0001 Not felt(I) 0.003 Not felt(I)
Forestville 2 (NC.NFVB) 0.0001 Not felt(I) 0.007 Not felt(I)
Lawrence Livermore National Laboratory, (BK.LLNL) 0.0001 Not felt(I) 0.002 Not felt(I)
CA: Novato; FS 1 (NP.1762) 0.0001 Not felt(I) 0.005 Not felt(I)
CA:Garberville;FS; Ground (NP.1591) 0.0001 Not felt(I) 0.008 Not felt(I)
Coyote Point (NC.JCPB) 0.0001 Not felt(I) 0.002 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
Boonville
CA
Weak(III)
Ukiah
CA
Weak(II)
Talmage
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
Bradford Property, Boonville, CA (BK.BONV) Weak(III)
Forest View Rd, Manchester, CA (NC.G007) Weak(III)
Beacon Light (NC.GBL) Weak(III)