Intensity Lab
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II

Max Est. MMI

26 km WNW of Ludlow, CA

Magnitude4.1
Depth1.4 km
Time 2026-03-27T22:13:14.860000Z UTC: 2026-03-27T22:13:14.860000Z
USGS ID ci41426656
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Ground Shaking Intensities — Interpolated ShakeMap MMI

3 sites
Location MMI
Fort Irwin
CA 		II
Barstow
CA 		II
Barstow Heights
CA 		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
Hector (CI.HEC) IV
Newberry Springs (CI.NBS) IV
Rodman Mountain (CI.RMM) III

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)
Fort Irwin
CA 		760 352
Barstow
CA 		760 352
Barstow Heights
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 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 +0.23 0.40 0.46
BSSA14 +0.23 0.39 0.45
CY14 +0.23 0.40 0.46
CB14 +0.23 0.39 0.45
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)
Hector (CI.HEC) 0.0357 IV 1.943 V
Newberry Springs (CI.NBS) 0.0241 IV 0.760 IV
Rodman Mountain (CI.RMM) 0.0051 I 0.187 III
Alvord Mountain (CI.AVM) 0.0037 I 0.133 II
Victorville (CI.VTV) 0.0035 I 0.118 II
Barstow Service Center (CI.RRX) 0.0027 I 0.127 II
Goat Mountain Astronomical Research Station (CI.GMA) 0.0026 I 0.122 II
Yucca Valley (CI.YUC) 0.0021 I 0.079 II
Wilsona 2 (CI.WLS2) 0.0020 I 0.082 II
Sunset Peak (CI.SUN) 0.0018 I 0.067 II
Barstow (CI.BAW) 0.0018 I 0.061 II
Mission Creek (CI.MSC) 0.0016 I 0.081 II
Mountain Pass (CI.MTP) 0.0015 I 0.037 II
Anaheim - Kraemer & La Palma (CE.13883) 0.0015 I 0.020 I
Granite Mountains Research Center (CI.GMR) 0.0015 I 0.030 II
Crystal Lake 2 (CI.XTL2) 0.0015 I 0.048 II
Hole In The Wall (CI.HIW) 0.0014 I 0.076 II
Adelanto Receiving (CI.ADO) 0.0014 I 0.059 II
Turquoise Mountain (CI.TUQ) 0.0013 I 0.046 II
Cajon Mountain (CI.CJM) 0.0012 I 0.057 II
Lucerne Valley 2 (CI.LUC2) 0.0012 I 0.072 II
Big Bear Solar Observatory (CI.BBR) 0.0011 I 0.030 II
Fish Rocks (CI.FSR) 0.0011 I 0.032 II
5030, Palmdale, CA (LT2) (NP.5030) 0.0010 I 0.047 II
Shoshone (CI.SHO) 0.0010 I 0.052 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.