M 4.0 - 54 km WNW of Petrolia, CA

  • 2024-12-09 07:15:42 (UTC)
  • 40.349°N 124.918°W
  • 10.0 km depth

ShakeAlert ®

 Contributed by EW last updated 2024-12-09 07:19:47 (UTC)
  • The data below are the most preferred data available
  • The data below have been reviewed by a scientist

Post ShakeAlert ® Message Summary

This report provides an overview of the performance of the ShakeAlert system during this event.

Reviewed: ShakeAlert Message issued at 2024-12-09 07:15:57.5 UTC. Results in this summary are preliminary. Alert may not have been sent to the shaken area.

Earthquake

Title
M 3.9 - 43.8 mi W of Fortuna
Time
2024-12-09 07:15:41.030 (UTC)
ShakeAlert Event ID
ew1733728550

Summary Report

ShakeAlert Messages Issued (after origin time):
Initial: 16.5 s
Peak: 16.5 s
Final: 26.7 s
ShakeAlert System Magnitude Estimates:
Initial: M 4.2
Peak: M 4.2
Final: M 4.0
ANSS report: 165 s after origin, M3.9
ShakeAlert System Location Accuracy:
Initial: 30 km (18 mi) WSW
Peak: 30 km (18 mi) WSW
Final: 28 km (17 mi) WSW
Wireless Emergency Alert:
Magnitude below threshold for WEA system.
WEA alerts are distributed to the MMI 4+ area if ShakeAlert Peak M >= 5.0
Number of Stations Reporting:
0 within 10km of epicenter
4 within 100km of epicenter
29 used in final ShakeAlert update
Nearby Cities
CityDistanceTime*Shaking (MMI**)
Fortuna 70 km (44 mi) — Not felt (I)
Eureka 81 km (50 mi) — Not felt (I)
Fort Bragg 141 km (87 mi) — Not felt (I)
Sacramento 356 km (221 mi) — Not felt (I)

Radius shaken before Message release: 59 km (36 mi)

  • Marker
    Initial MMI 3
    0.0 s
    10.0 s
    20.0 s
    50 km
    30 mi
    Figure 1. ShakeAlert initial earthquake location (black dot). Star is ANSS earthquake epicenter. Polygon approximates the outer range for felt ground motion. If shown, red circle is front of peak shaking when the Message was released***. Shaking takes 10 s to expand from circle to circle.
  • Marker
    MMI 3
    MMI 4
    50 km
    30 mi
    Figure 2. Polygons show shaking intensity contours for the peak magnitude estimate. Shaking of MMI 3 or less is often not felt. Star shows the ANSS earthquake epicenter.

Footnotes

  1. * Time — Time from message release to predicted S-wave arrival at the location. "—" for weak or imperceptable shaking.
  2. ** MMI — Modified Mercalli Intensity: a numeric shaking severity scale
  3. *** For earthquakes deeper than ~15 km, the ShakeAlert Message may be available before peak shaking reaches the surface.