M 4.9 - 7km WNW of Rio Dell, CA

  • 2022-12-20 10:39:02 (UTC)
  • 40.523°N 124.188°W
  • 26.6 km depth

ShakeAlert ®

 Contributed by EW last updated 2022-12-20 10:42:58 (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 2022-12-20 10:39:02.6 UTC.

Earthquake

Title
M 4.6 - 3.7 mi W of Rio Dell
Time
2022-12-20 10:39:02.600 (UTC)
ShakeAlert Event ID
ew1671532750

Summary Report

ShakeAlert Messages Issued (after origin time):
Initial: 7.9 s
Peak: 44.0 s
Final: 44.0 s
ShakeAlert System Magnitude Estimates:
Initial: M 4.5
Peak: M 4.9
Final: M 4.9
ANSS report: 120 s after origin, M4.6
ShakeAlert System Location Accuracy:
Initial: 3 km (2 mi) SSE
Peak: 6 km (3 mi) ENE
Final: 6 km (3 mi) ENE
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
8 within 100km of epicenter
6 used in final ShakeAlert update
Nearby Cities
CityDistanceTime*Shaking (MMI**)
Rio Dell 6 km (4 mi) ~0.0 s Light (IV)
Eureka 32 km (20 mi) — Weak (III)
Fort Bragg 123 km (76 mi) — Not felt (I)
Sacramento 315 km (196 mi) — Not felt (I)

Radius shaken before Message release: 15 km (9 mi)

  • Marker
    Initial MMI 3
    0.0 s
    10.0 s
    20.0 s
    30 km
    20 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 5
    MMI 4
    MMI 3
    30 km
    20 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.