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Intensity Lab
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Max Est. MMI

M4.6 earthquake · shaking intensity by town 1 km SE of Boulder Creek, CA

Magnitude4.6
Depth10.4 km
Time 2026-04-02T08:41:25.520000Z UTC: 2026-04-02T08:41:25.520000Z
USGS ID nc75337442
ShakeMap View USGS ↗

Shaking Animations

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

2 sites
Location Type Intensity at site Animation Ground motion
Ben Lomond Mountain Station · Tabletop Observed Strong(VI) station record
Brookdale City · Tabletop Simulated Moderate(V) USGS ShakeMap

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)
Brookdale
CA 		760 370
Boulder Creek
CA 		760 391
Ben Lomond
CA 		760 408
Bonny Doon
CA 		760 613
Lompico
CA 		760 460
Mount Hermon
CA 		760 409
Felton
CA 		760 413
Pasatiempo
CA 		760 469
Scotts Valley
CA 		760 404
Santa Cruz
CA 		760 436
Live Oak
CA 		760 388
Soquel
CA 		760 352
Twin Lakes
CA 		760 353
Capitola
CA 		760 292
Aptos
CA 		760 386
Rio Del Mar
CA 		760 379
Seacliff
CA 		760 377

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 +0.15 0.46 0.49
BSSA14 +0.23 0.46 0.51
CY14 +0.23 0.46 0.51
CB14 +0.21 0.46 0.51
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)
Ben Lomond Mountain (NC.JBNB) 0.5816 Severe(VIII) 9.749 Strong(VI)
Cotoni-Coast Dairies (NC.JCD) 0.2001 Strong(VI) 9.132 Moderate(V)
UCSC Arboretum (NC.JAR) 0.0843 Moderate(V) 2.869 Light(IV)
Pescadero #2 (NC.JPSB) 0.0617 Moderate(V) 2.277 Light(IV)
Cabrillo College (NC.JCC) 0.0544 Light(IV) 1.875 Light(IV)
Scotts Valley (NC.JSV) 0.0534 Light(IV) 1.377 Light(IV)
Bear Creek Rd (NC.JBR) 0.0428 Light(IV) 1.526 Light(IV)
Bear Gulch Road #2 (NC.JBG) 0.0421 Light(IV) 2.094 Light(IV)
Peninsula Open Space; Pescadero, CA (BK.PESC) 0.0417 Light(IV) 1.045 Weak(III)
Peters Creek (NC.JPE) 0.0341 Light(IV) 1.882 Light(IV)
Filoli Center (NP.1752) 0.0310 Light(IV) 0.985 Weak(III)
Black Mountain #3 (NC.JBMB) 0.0309 Light(IV) 1.520 Light(IV)
Sunnyvale Rod and Gun Club (NP.1862) 0.0277 Light(IV) 1.343 Light(IV)
Mountain View FS 3 (NP.1775) 0.0263 Light(IV) 1.569 Light(IV)
St. Joseph Seminary (NC.JSJ) 0.0248 Weak(III) 0.956 Weak(III)
Stanford Telescope (NC.JSFB) 0.0234 Weak(III) 1.326 Light(IV)
Addison School (NP.1853) 0.0207 Weak(III) 1.100 Weak(III)
Mount Umunhum (BK.UMUN) 0.0203 Weak(III) 0.539 Weak(III)
Saratoga Golf Course (NC.JSGB) 0.0201 Weak(III) 1.146 Weak(III)
St Josephs Hill (NC.JJO) 0.0187 Weak(III) 0.986 Weak(III)
Fire Station 27 (NP.1858) 0.0183 Weak(III) 0.736 Weak(III)
Foothills Park (NC.JFP) 0.0182 Weak(III) 0.770 Weak(III)
Las Palmas Park (NP.1791) 0.0172 Weak(III) 1.253 Weak(III)
Cahill Ridge (NC.JCH) 0.0170 Weak(III) 0.786 Weak(III)
Jasper Ridge Ecological Reserve (BK.JASP) 0.0164 Weak(III) 0.937 Weak(III)
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

17 sites
Location MMI Description
Brookdale
CA 		Moderate(V)
Boulder Creek
CA 		Moderate(V)
Ben Lomond
CA 		Moderate(V)
Bonny Doon
CA 		Moderate(V)
Lompico
CA 		Light(IV)
Mount Hermon
CA 		Light(IV)
Felton
CA 		Light(IV)
Pasatiempo
CA 		Light(IV)
Scotts Valley
CA 		Light(IV)
Santa Cruz
CA 		Light(IV)
Live Oak
CA 		Light(IV)
Soquel
CA 		Light(IV)
Twin Lakes
CA 		Light(IV)
Capitola
CA 		Light(IV)
Aptos
CA 		Light(IV)
Rio Del Mar
CA 		Light(IV)
Seacliff
CA 		Light(IV)