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Intensity Lab
II

Max Est. MMI

M5.0 earthquake · shaking intensity by town 114 km W of Petrolia, CA

Magnitude5.0
Depth2.1 km
Time 2026-11-05T04:56:01.430000Z UTC: 2026-11-05T04:56:01.430000Z
USGS ID nc75462637
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)
Ferndale
CA 		760 273
Fortuna
CA 		760 418
Humboldt Hill
CA 		760 370

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, estimated 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 0.35 0.39
BSSA14 +0.11 0.29 0.31
CY14 +0.24 0.43 0.49
CB14 +0.18 0.35 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)
Thorn Junction (NC.KTJ) 0.0047 Weak(II) 0.162 Weak(II)
Fire Station (NP.1023) 0.0044 Weak(II) 0.224 Weak(II)
College of the Redwoods (NP.1582) 0.0038 Weak(II) 0.236 Weak(II)
Walker Ranch; near Petrolia CA (BK.WLKR) 0.0036 Weak(II) 0.211 Weak(II)
Paradise Ridge (BK.PRDS) 0.0031 Weak(II) 0.115 Weak(II)
Punta Gorda, Petrolia, CA (BK.PETL) 0.0030 Weak(II) 0.154 Weak(II)
South Bay School (NP.1581) 0.0029 Weak(II) 0.128 Weak(II)
Sproul Creek (BK.SPRL) 0.0026 Weak(II) 0.149 Weak(II)
Loleta Fire Station (NP.1586) 0.0017 Weak(II) 0.078 Weak(II)
Briceland Vineyard, Redway, CA (BK.BRIC) 0.0016 Weak(II) 0.061 Weak(II)
Big Mountain (BK.BIGM) 0.0014 Weak(II) 0.046 Not felt(I)
Cape Town (NC.KCT) 0.0014 Weak(II) 0.111 Weak(II)
Lost Coast Ranch (NP.1725) 0.0013 Weak(II) 0.081 Weak(II)
Slide Mountain #2 (NC.KSM) 0.0013 Not felt(I) 0.058 Weak(II)
Rainbow Ridge, Humboldt, CA (BK.RBOW) 0.0011 Not felt(I) 0.086 Weak(II)
Bunker Hill, NOAA Radar (NP.1584B) 0.0011 Not felt(I) 0.066 Weak(II)
Needle Rock (NC.KNR) 0.0011 Not felt(I) 0.037 Not felt(I)
Garberville CALFire station (NP.1591) 0.0008 Not felt(I) 0.046 Not felt(I)
Krueger Creek (BK.KRUG) 0.0008 Not felt(I) 0.037 Not felt(I)
Kneeland/Ashfield Ridge (BK.KNEE) 0.0008 Not felt(I) 0.051 Not felt(I)
Hayfork Bally (NC.KHBB) 0.0007 Not felt(I) 0.013 Not felt(I)
Usal Creek (BK.USAL) 0.0006 Not felt(I) 0.028 Not felt(I)
Mail Ridge (NC.KMR) 0.0006 Not felt(I) 0.042 Not felt(I)
Grasshopper Mountain (BK.GHOP) 0.0006 Not felt(I) 0.043 Not felt(I)
Black Lassic (BK.BLAS) 0.0005 Not felt(I) 0.030 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
Ferndale
CA 		Weak(II)
Fortuna
CA 		Weak(II)
Humboldt Hill
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
Lost Coast Ranch (NP.1725) Weak(II)
Cape Town (NC.KCT) Weak(II)
Punta Gorda, Petrolia, CA (BK.PETL) Weak(II)