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Intensity Lab
II

Max Est. MMI

M3.6 earthquake · shaking intensity by town 2 km E of Oak Harbor, Washington

Magnitude3.6
Depth25.4 km
Time 2026-07-02T06:35:47.540000Z UTC: 2026-07-02T06:35:47.540000Z
USGS ID uw714040221
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)
Oak Harbor
WA 		760 458
Ault Field
WA 		760 410
Coupeville
WA 		760 509

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 -0.10 0.33 0.34
BSSA14 +0.04 0.29 0.29
CY14 -0.33 0.45 0.55
CB14 -0.19 0.37 0.42
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)
Pacific Rim Institute, Coupeville, WA, USA (UW.PRIN) 0.0203 Weak(III) 0.425 Weak(III)
North Whidbey Fire, Oak Harbor, WA, USA (UW.OAKH) 0.0081 Weak(III) 0.229 Weak(II)
Fidalgo Island, WA, USA (UW.ERIE) 0.0076 Weak(III) 0.205 Weak(II)
Seahawks 6, Seattle, WA, USA (UW.HWK6) 0.0076 Weak(III) 0.152 Weak(II)
Lake Cavanaugh, Mt Vernon, WA, USA (UW.LKCAV) 0.0073 Weak(III) 0.114 Weak(II)
Cougar Creek Elementary School, Arlington, WA, USA (UW.CUGR) 0.0069 Weak(III) 0.104 Weak(II)
Elger Bay Elementary School, Camano, WA, USA (UW.ELGR) 0.0065 Weak(III) 0.209 Weak(II)
North County Fire, Warm Beach, WA, USA (UW.WRMB) 0.0048 Weak(II) 0.150 Weak(II)
Conway School, Mount Vernon, WA, USA (UW.CONW) 0.0047 Weak(II) 0.095 Weak(II)
Skagit Valley CC, WA, USA (UW.SVOH) 0.0046 Weak(II) 0.174 Weak(II)
La Conner, WA, USA (UW.HILL) 0.0039 Weak(II) 0.112 Weak(II)
Granite Falls Middle School, Granite Falls, WA, USA (UW.GRNT) 0.0039 Weak(II) 0.087 Weak(II)
Samish Elementary School, Sedro-Woolley, WA, USA (UW.SMSH) 0.0037 Weak(II) 0.105 Weak(II)
Roche Harbor Airport, San Juan Island, WA, USA (UW.RNWY) 0.0037 Weak(II) 0.113 Weak(II)
Skagit County Fire District 6, Burlington, WA, USA (UW.SKGF) 0.0037 Weak(II) 0.132 Weak(II)
North County Fire, Stanwood, WA, USA (UW.STNW) 0.0036 Weak(II) 0.070 Weak(II)
Deming, WA, USA (UW.DMNG) 0.0033 Weak(II) 0.098 Weak(II)
Tolt Reservoir, Control House, WA, USA (UW.TLW1) 0.0033 Weak(II) 0.052 Not felt(I)
Friday Harbor, WA, USA (UW.SJIF) 0.0032 Weak(II) 0.088 Weak(II)
Sedro-Woolley City Hall, Sedro-Woolley, WA, USA (UW.SDRO) 0.0027 Weak(II) 0.061 Weak(II)
Brown Road Station 2, Whatcom County, WA, USA (UW.TULA) 0.0025 Weak(II) 0.059 Weak(II)
Central Whidbey Island Fire, Greenbank, WA, USA (UW.CWFG) 0.0023 Weak(II) 0.089 Weak(II)
Edison Elementary School, Bow, WA, USA (UW.EDSN) 0.0022 Weak(II) 0.116 Weak(II)
Olga, Orcas Island, WA, USA (UW.OLGA) 0.0021 Weak(II) 0.042 Not felt(I)
Machias Elementary School, Machias, WA, USA (UW.MACH) 0.0020 Weak(II) 0.044 Not felt(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.

Ground Shaking Intensities — Interpolated ShakeMap MMI

3 sites
Location MMI Description
Oak Harbor
WA 		Weak(II)
Ault Field
WA 		Weak(II)
Coupeville
WA 		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
Skagit Valley CC, WA, USA (UW.SVOH) Weak(II)
North Whidbey Fire, Oak Harbor, WA, USA (UW.OAKH) Weak(III)
Pacific Rim Institute, Coupeville, WA, USA (UW.PRIN) Weak(III)