Intensity Lab
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III

Max Est. MMI

18 km NE of Upper Lake, CA

Magnitude3.7
Depth7.3 km
Time 2026-03-26T17:24:54.900000Z UTC: 2026-03-26T17:24:54.900000Z
USGS ID nc75333407
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Ground Shaking Intensities — Interpolated ShakeMap MMI

3 sites
Location MMI
Upper Lake
CA 		III
Nice
CA 		III
Lucerne
CA 		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
Bevans Ridge (BK.BEVN) III
Trough Springs/Crackerbox Ridge, CA 95979 (BK.GTSB) III
Hogback Ridge (NC.GHGB) 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)
Upper Lake
CA 		760 228
Nice
CA 		760 733
Lucerne
CA 		760 228

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 0.38 0.38
BSSA14 +0.08 0.37 0.38
CY14 +0.08 0.37 0.38
CB14 +0.08 0.37 0.37
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)
Hogback Ridge (NC.GHGB) 0.0093 II 0.280 III
Trough Springs/Crackerbox Ridge, CA 95979 (BK.GTSB) 0.0064 II 0.198 III
Bevans Ridge (BK.BEVN) 0.0054 I 0.239 III
Cow Mountain (NC.GCWB) 0.0028 I 0.118 II
Round Top Mountain (NC.GRT) 0.0011 I 0.047 II
Barra Winery, Redwood Valley, CA (BK.BARR) 0.0008 I 0.029 II
Grizzly Island (NC.NGI) 0.0008 I 0.008 I
Thermalito Afterbay Dam (WR.THER) 0.0006 I 0.006 I
Lloyd Lowery (NC.NLL) 0.0005 I 0.016 I
Clifton Court Forebay South (WR.CLFS) 0.0004 I 0.011 I
Lawrence Livermore National Laboratory, (BK.LLNL) 0.0004 I 0.002 I
Navarro Ridge (NC.GNR) 0.0004 I 0.022 I
Hamilton Opening (NC.GHO) 0.0004 I 0.022 I
Circle K Ranch (WR.CKR) 0.0004 I 0.004 I
Van Arsdale (NC.GVA) 0.0003 I 0.014 I
Beacon Light (NC.GBL) 0.0003 I 0.016 I
Pine Mountain #1 (NC.GPM) 0.0003 I 0.012 I
Wonder Ranch (NC.GWR) 0.0003 I 0.018 I
Bald Mountain (NC.NBM) 0.0003 I 0.015 I
Hull Mountain (BK.HULL) 0.0003 I 0.024 I
Snow Mountain (NC.GSN) 0.0003 I 0.016 I
Bradford Ranch, Boonville, CA (BK.BONV) 0.0003 I 0.014 I
Spanish Creek (BK.SPAN) 0.0003 I 0.015 I
Wildwood Ranch (NC.GWW) 0.0002 I 0.016 I
CA: Danville; Fire Station (NP.1690) 0.0002 I 0.003 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.