Intensity Lab
← All events
II

Max Est. MMI

27 km W of Petrolia, CA

Magnitude3.7
Depth19.6 km
Time 2026-03-17T12:56:18.200000Z UTC: 2026-03-17T12:56:18.200000Z
USGS ID nc75328787
ShakeMap View USGS ↗

Ground Shaking Intensities — Interpolated ShakeMap MMI

3 sites
Location MMI
Ferndale
CA 		II
Rio Dell
CA 		II
Fortuna
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
Punta Gorda, Petrolia, CA (BK.PETL) II
Walker Ranch; near Petrolia CA (BK.WLKR) II
Lost Coast Ranch (NP.1725) II

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).

Show ▼

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
Rio Dell
CA 		760 468
Fortuna
CA 		760 418

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 +0.12 0.36 0.38
BSSA14 +0.12 0.36 0.38
CY14 +0.12 0.35 0.37
CB14 +0.11 0.34 0.36
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)
Pringle Ridge (NC.KPR) 0.0042 I 0.136 II
Rainbow Ridge, Humboldt, CA (BK.RBOW) 0.0025 I 0.117 II
Fire Station (NP.1023) 0.0017 I 0.082 II
Paradise Ridge (BK.PRDS) 0.0016 I 0.040 II
Thorn Junction (NC.KTJ) 0.0014 I 0.034 II
Punta Gorda, Petrolia, CA (BK.PETL) 0.0014 I 0.079 II
Grasshopper Mountain (BK.GHOP) 0.0014 I 0.043 II
Briceland Vineyard, Redway, CA (BK.BRIC) 0.0011 I 0.031 II
Burgh Ranch (NC.KBU) 0.0011 I 0.036 II
Bunker Hill, NOAA Radar (NP.1584B) 0.0010 I 0.052 II
Walker Ranch; near Petrolia CA (BK.WLKR) 0.0009 I 0.067 II
Lost Coast Ranch (NP.1725) 0.0009 I 0.084 II
Garberville CALFire station (NP.1591) 0.0009 I 0.033 II
Black Lassic (BK.BLAS) 0.0008 I 0.025 I
Sproul Creek (BK.SPRL) 0.0005 I 0.023 I
Usal Creek (BK.USAL) 0.0005 I 0.016 I
Jewett Creek (BK.JEWT) 0.0005 I 0.019 I
Bald Jesse, Humboldt County, CA (BK.BJES) 0.0004 I 0.014 I
Loleta Fire Station (NP.1586) 0.0003 I 0.017 I
College of the Redwoods (NP.1582) 0.0002 I 0.009 I
Hales Grove, Mendocino, CA (BK.HALS) 0.0002 I 0.006 I
Round Valley Indian Tribe, Mendocino County, CA (BK.RVIT) 0.0002 I 0.006 I
Big Mountain (BK.BIGM) 0.0001 I 0.005 I
Bell Springs #3 (NC.KBSB) 0.0001 I 0.006 I
Long Ridge (NC.KLR) 0.0001 I 0.005 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.