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Intensity Lab
II

Max Est. MMI

M4.4 earthquake · shaking intensity by town 31 km NNW of Covelo, CA

Magnitude4.4
Depth7.3 km
Time 2026-08-05T22:21:57.380000Z UTC: 2026-08-05T22:21:57.380000Z
USGS ID nc75412157
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)
Covelo
CA 		760 294
Redway
CA 		760 352
Laytonville
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 -0.05 0.28 0.28
BSSA14 -0.07 0.28 0.29
CY14 -0.02 0.26 0.26
CB14 -0.03 0.26 0.26
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)
Long Ridge (NC.KLR) 0.0229 Weak(III) 1.108 Weak(III)
Round Valley Indian Tribe, Mendocino County, CA (BK.RVIT) 0.0142 Weak(III) 0.704 Weak(III)
Black Lassic (BK.BLAS) 0.0096 Weak(III) 0.431 Weak(III)
Bell Springs #3 (NC.KBSB) 0.0090 Weak(III) 0.387 Weak(III)
Hoaglin-Zenia Elementary School (NC.KZE) 0.0078 Weak(III) 0.442 Weak(III)
Hales Grove, Mendocino, CA (BK.HALS) 0.0075 Weak(III) 0.349 Weak(III)
Jewett Creek (BK.JEWT) 0.0072 Weak(III) 0.339 Weak(III)
Garberville CALFire station (NP.1591) 0.0063 Weak(III) 0.313 Weak(III)
Pringle Ridge (NC.KPR) 0.0042 Weak(II) 0.186 Weak(II)
Needle Rock (NC.KNR) 0.0041 Weak(II) 0.197 Weak(II)
Grasshopper Mountain (BK.GHOP) 0.0034 Weak(II) 0.162 Weak(II)
Iron Peak (NC.KIP) 0.0034 Weak(II) 0.095 Weak(II)
Big Mountain (BK.BIGM) 0.0032 Weak(II) 0.129 Weak(II)
Usal Creek (BK.USAL) 0.0029 Weak(II) 0.202 Weak(II)
Paradise Ridge (BK.PRDS) 0.0028 Weak(II) 0.163 Weak(II)
Fire Station (NP.1023) 0.0028 Weak(II) 0.126 Weak(II)
Sproul Creek (BK.SPRL) 0.0028 Weak(II) 0.156 Weak(II)
Big Hunter Mountain, Trinity County (BK.HUNT) 0.0028 Weak(II) 0.261 Weak(II)
Pickett Peak (NC.KPPB) 0.0027 Weak(II) 0.101 Weak(II)
Slide Mountain #2 (NC.KSM) 0.0027 Weak(II) 0.145 Weak(II)
Tule Creek, Hayfork, CA (BK.HAYF) 0.0026 Weak(II) 0.135 Weak(II)
Briceland Vineyard, Redway, CA (BK.BRIC) 0.0026 Weak(II) 0.109 Weak(II)
Rainbow Ridge, Humboldt, CA (BK.RBOW) 0.0024 Weak(II) 0.130 Weak(II)
Walker Ranch; near Petrolia CA (BK.WLKR) 0.0022 Weak(II) 0.174 Weak(II)
Bald Jesse, Humboldt County, CA (BK.BJES) 0.0022 Weak(II) 0.143 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
Covelo
CA 		Weak(II)
Redway
CA 		Weak(II)
Laytonville
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
Long Ridge (NC.KLR) Light(IV)
Round Valley Indian Tribe, Mendocino County, CA (BK.RVIT) Weak(III)
Jewett Creek (BK.JEWT) Weak(III)