15km WSW of Ferndale, CA

Magnitude6.4

Depth17.9 km

Time 2022-12-20T10:34:24.770000Z UTC: 2022-12-20T10:34:24.770000Z

USGS ID nc73821036

ShakeMap View USGS ↗

Ground Shaking Intensities — Interpolated ShakeMap MMI

18 sites

Location	MMI Description	Dist (km)	Dist (mi)
Hydesville CA	Very Strong(VII)	28	17
Rio Dell CA	Very Strong(VII)	27	17
Fortuna CA	Strong(VI)	24	15
Ferndale CA	Strong(VI)	15	9
Humboldt Hill CA	Strong(VI)	30	19
Bayview CA	Strong(VI)	34	21
Cutten CA	Strong(VI)	36	22
Myrtletown CA	Strong(VI)	38	24
Pine Hills CA	Strong(VI)	33	21
Bayside CA	Moderate(V)	47	29
Eureka CA	Moderate(V)	38	24
Arcata CA	Moderate(V)	48	30
Blue Lake CA	Moderate(V)	54	34
Redway CA	Moderate(V)	68	42
McKinleyville CA	Moderate(V)	54	34
Westhaven-Moonstone CA	Light(IV)	64	40
Hayfork CA	Light(IV)	105	65
Willow Creek CA	Light(IV)	81	50

Shaking Animations

Simulated bowling pin shaking at each city’s intensity level. Videos appear as they finish rendering.

3 sites

Location	Type	MMI Description	Animation
Cape Town	Observed data	Very Strong(VII)	Download
Decay: Sacramento direction	Ground Motion Decay	Very Strong(VII)	Download
Ferndale	Simulated	Strong(VI)	Download

Seismic Station Observed MMI

MMI values are derived directly from observed ground motion measurements at seismic stations and are not spatially interpolated.

35 stations

Station	Network	MMI Description	Dist (km)	Dist (mi)
Rio Dell (CE.89462)	CE	Severe(VIII)	27	17
Kneeland/Ashfield Ridge (BK.KNEE)	BK	Very Strong(VII)	49	30
CA:Eureka;Coll of the Redwoods (NP.1582)	NP	Very Strong(VII)	27	17
Fortuna (CE.89255)	CE	Very Strong(VII)	25	16
CA:Eureka;South Bay School (NP.1581)	NP	Very Strong(VII)	30	19
Cape Town (NC.KCT)	NC	Very Strong(VII)	9	6
Fortuna (CE.89486)	CE	Very Strong(VII)	24	15
CA:Loleta;FS (NP.1586)	NP	Very Strong(VII)	22	14
Bald Jesse, Humboldt County, CA (BK.BJES)	BK	Strong(VI)	46	29
CA:Ferndale;FS (NP.1023)	NP	Strong(VI)	15	9
Eureka (CE.89641)	CE	Strong(VI)	38	24
Burgh Ranch (NC.KBU)	NC	Strong(VI)	57	35
Cooskie Peak (NC.KCO)	NC	Strong(VI)	33	21
Pringle Ridge (NC.KPR)	NC	Strong(VI)	46	29
Horse Mountain (NC.KHMB)	NC	Strong(VI)	70	43
Cold Springs (NC.KCSB)	NC	Strong(VI)	77	48
Mount Pierce (NC.KMPB)	NC	Strong(VI)	28	17
Rainbow Ridge, Humboldt, CA (BK.RBOW)	BK	Moderate(V)	34	21
Paradise Ridge (BK.PRDS)	BK	Moderate(V)	57	35
CA:Ferndale;Bunker Hill NOAA (NP.1584B)	NP	Moderate(V)	11	7
Mail Ridge (NC.KMR)	NC	Moderate(V)	70	43
CA:Garberville;FS (NP.1591)	NP	Moderate(V)	71	44
Punta Gorda, Petrolia, CA (BK.PETL)	BK	Moderate(V)	27	17
Briceland Vineyard, Redway, CA (BK.BRIC)	BK	Moderate(V)	64	40
Tule Creek, Hayfork, CA (BK.HAYF)	BK	Moderate(V)	101	63
Chalk Rock #3 (NC.KCR)	NC	Moderate(V)	52	32
Hayfork Bally (NC.KHBB)	NC	Light(IV)	103	64
Trinidad Head (NC.KTD)	NC	Light(IV)	63	39
Baker Fire Station, Cottonwood, CA (BK.BAKR)	BK	Light(IV)	166	103
Hat Creek Radio Astronomy Obs., Cassel, CA, USA (BK.HATC)	BK	Light(IV)	252	157
Round Valley Indian Tribe, Mendocino County, CA (BK.RVIT)	BK	Light(IV)	112	70
Shelter Cove (CE.89688)	CE	Light(IV)	62	39
Grey Butte (Mt Shasta) (NC.LGY)	NC	Light(IV)	208	129
Burney Mountain (NC.LBU)	NC	Light(IV)	236	147
Willits (CE.79668)	CE	Light(IV)	156	97

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)	Source	Dist (km)	Dist (mi)
Hydesville CA	760	468	CGS Geology	28	17
Rio Dell CA	760	468	CGS Geology	27	17
Fortuna CA	760	418	CGS Geology	24	15
Ferndale CA	760	273	CGS Geology	15	9
Humboldt Hill CA	760	370	CGS Geology	30	19
Bayview CA	760	350	CGS Geology	34	21
Cutten CA	760	359	CGS Geology	36	22
Myrtletown CA	760	354	CGS Geology	38	24
Pine Hills CA	760	369	CGS Geology	33	21
Bayside CA	760	357	CGS Geology	47	29
Eureka CA	760	280	CGS Geology	38	24
Arcata CA	760	351	CGS Geology	48	30
Blue Lake CA	760	352	CGS Geology	54	34
Redway CA	760	352	CGS Geology	68	42
McKinleyville CA	760	373	CGS Geology	54	34
Westhaven-Moonstone CA	760	411	CGS Geology	64	40
Hayfork CA	760	351	CGS Geology	105	65
Willow Creek CA	760	733	CGS Geology	81	50

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 — Est. Vs30

GMPEs use the Est. Vs30 values shown in the table above. ShakeMap values are independent of 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 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 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	N Stations
ASK14	+1.34	0.82	1.57	168
BSSA14	+1.50	0.75	1.68	168
CY14	+1.28	0.80	1.50	168
CB14	+1.26	0.82	1.50	168

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	Dist (km)	PGA (g)	MMI (PGA)	PGV (cm/s)	MMI (PGV)
Rio Dell (CE.89462)	27	1.4387	Very Strong(VII)	63.425	Extreme(X)
Fortuna (CE.89255)	25	0.8010	Strong(VI)	34.755	Violent(IX)
CA:Eureka;Coll of the Redwoods (NP.1582)	27	0.4536	Strong(VI)	34.115	Violent(IX)
Fortuna (CE.89486)	24	0.3938	Strong(VI)	28.695	Severe(VIII)
CA:Loleta;FS (NP.1586)	22	0.3000	Moderate(V)	25.784	Severe(VIII)
Eureka (CE.89641)	38	0.2959	Moderate(V)	21.361	Severe(VIII)
CA:Eureka;South Bay School (NP.1581)	30	0.2748	Moderate(V)	32.524	Violent(IX)
CA:Ferndale;FS (NP.1023)	15	0.2561	Moderate(V)	22.278	Severe(VIII)
CA:Ferndale;Bunker Hill NOAA (NP.1584B)	11	0.2212	Moderate(V)	10.324	Very Strong(VII)
Paradise Ridge (BK.PRDS)	57	0.1806	Moderate(V)	9.706	Very Strong(VII)
Kneeland/Ashfield Ridge (BK.KNEE)	49	0.1636	Moderate(V)	39.187	Violent(IX)
Pringle Ridge (NC.KPR)	46	0.1402	Moderate(V)	15.552	Severe(VIII)
Burgh Ranch (NC.KBU)	57	0.1382	Moderate(V)	18.543	Severe(VIII)
Bald Jesse, Humboldt County, CA (BK.BJES)	46	0.1254	Moderate(V)	21.984	Severe(VIII)
Horse Mountain (NC.KHMB)	70	0.1253	Moderate(V)	15.092	Severe(VIII)
Cape Town (NC.KCT)	9	0.1239	Moderate(V)	30.028	Violent(IX)
Mount Pierce (NC.KMPB)	28	0.1237	Moderate(V)	11.679	Very Strong(VII)
Punta Gorda, Petrolia, CA (BK.PETL)	27	0.1236	Moderate(V)	8.521	Very Strong(VII)
Cooskie Peak (NC.KCO)	33	0.1201	Moderate(V)	15.272	Severe(VIII)
Tule Creek, Hayfork, CA (BK.HAYF)	101	0.1037	Moderate(V)	8.198	Very Strong(VII)
CA:Garberville;FS (NP.1591)	71	0.0950	Moderate(V)	9.032	Very Strong(VII)
Cold Springs (NC.KCSB)	77	0.0868	Moderate(V)	12.725	Very Strong(VII)
Rainbow Ridge, Humboldt, CA (BK.RBOW)	34	0.0795	Moderate(V)	10.511	Very Strong(VII)
Briceland Vineyard, Redway, CA (BK.BRIC)	64	0.0752	Moderate(V)	7.824	Very Strong(VII)
Mail Ridge (NC.KMR)	70	0.0721	Moderate(V)	9.469	Very Strong(VII)

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.