VII

Max Est. MMI

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 ↗

Shaking Animations

Simulated bowling pin shaking at each city’s intensity level. Videos appear as they finish rendering. The ground motion behind each video is under Ground Motion Records.

3 sites

Location	Type	Intensity at site	Animation	Ground motion
Cape Town	Station · Tabletop Observed	Very Strong(VII) station record	Download Produced 2026-10-04T00:12:17.107442Z	Data files
Decay: Sacramento direction	Decay · Tabletop Simulated	Very Strong(VII) USGS ShakeMap, 5 km site	Download Produced 2026-10-03T01:26:09.217733Z	Data files
Ferndale	City · Tabletop Simulated	Very Strong(VII) USGS ShakeMap	Download Produced 2026-10-03T04:44:41.631716Z	Data files

Ground Motion Records

The shaking each animation was drawn from: acceleration, velocity and displacement in three directions. The shaded band marks the part the animation shows.

Download all (zip)

City · Simulated — Ferndale, CA

Used by the Tabletop video

A physics-based simulation of this earthquake (SCEC Broadband Platform) at this site: one realization, not an average.

Acceleration, velocity and displacement seismograms for city animation

Site	PGA (g)	PGV (cm/s)	PGD (cm)	Data files
Ferndale, CA	0.2603	53.22	12.86	Acceleration · Velocity · Displacement

Peak values are horizontal (the larger of north–south and east–west) over the whole record. Time zero: rupture origin time (simulation time 0).

Station · Observed — NC.KCT (Cape Town)

Used by the Tabletop video

Recorded by a seismic station during this earthquake, with the instrument response removed.

Acceleration, velocity and displacement seismograms for station animation

Site	PGA (g)	PGV (cm/s)	PGD (cm)	Data files
NC.KCT (Cape Town)	0.1194	29.98	5.70	Acceleration · Velocity · Displacement

Peak values are horizontal (the larger of north–south and east–west) over the whole record. Time zero: earthquake origin time.

Decay · Simulated — 5 km from the epicenter, 50 km from the epicenter, 100 km from the epicenter

Used by the Tabletop video

A physics-based simulation of this earthquake (SCEC Broadband Platform) at this site: one realization, not an average.

Acceleration, velocity and displacement seismograms for decay animation

Site	PGA (g)	PGV (cm/s)	PGD (cm)	Data files
5 km from the epicenter	0.2796	19.02	4.47	Acceleration · Velocity · Displacement
50 km from the epicenter	0.0596	4.51	1.98	Acceleration · Velocity · Displacement
100 km from the epicenter	0.0243	2.26	0.78	Acceleration · Velocity · Displacement

Peak values are horizontal (the larger of north–south and east–west) over the whole record. Time zero: rupture origin time (simulation time 0).

About these files

Each file is plain text in the SCEC Broadband Platform layout. Lines starting with # are a header describing the earthquake, the site, where the motion came from, how it was processed, its peak values, and which part the animation shows. Then come four columns: time (s), north–south, east–west, and up–down. North–south comes before east–west.

Units: acceleration in cm/s², velocity in cm/s, displacement in cm. The zip also contains the plots and a README.

To read a file in Python: t, ns, ew, ud = numpy.loadtxt("file.acc.bbp", comments="#", unpack=True). A spreadsheet can open it as whitespace-delimited text.

These records explain what the animations show. A single simulation, one station’s record, or a synthetic scaled to one value is not an engineering estimate of ground motion at a site.

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

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)
College 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)
Loleta Fire Station (NP.1586)	22	0.3000	Moderate(V)	25.784	Severe(VIII)
Eureka (CE.89641)	38	0.2959	Moderate(V)	21.361	Severe(VIII)
South Bay School (NP.1581)	30	0.2748	Moderate(V)	32.524	Violent(IX)
Fire Station (NP.1023)	15	0.2561	Moderate(V)	22.278	Severe(VIII)
Bunker Hill, NOAA Radar (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)
Garberville CALFire station (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.

Ground Shaking Intensities — Interpolated ShakeMap MMI

18 sites

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

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
Fortuna (CE.89255)	CE	Very Strong(VII)	25	16
College of the Redwoods (NP.1582)	NP	Very Strong(VII)	27	17
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
Loleta Fire Station (NP.1586)	NP	Very Strong(VII)	22	14
Bald Jesse, Humboldt County, CA (BK.BJES)	BK	Strong(VI)	46	29
Fire Station (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
Horse Mountain (NC.KHMB)	NC	Strong(VI)	70	43
Pringle Ridge (NC.KPR)	NC	Strong(VI)	46	29
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
Bunker Hill, NOAA Radar (NP.1584B)	NP	Moderate(V)	11	7
Mail Ridge (NC.KMR)	NC	Moderate(V)	70	43
Garberville CALFire station (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 #2 (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
Willits (CE.79668)	CE	Light(IV)	156	97
Burney Mountain (NC.LBU)	NC	Light(IV)	236	147
Grey Butte (Mt Shasta) (NC.LGY)	NC	Light(IV)	208	129