M 4.3 - 2km E of Carson, CA

  • 2021-09-18 02:58:34 (UTC)
  • 33.831°N 118.264°W
  • 11.9 km depth

ShakeAlert ®

 Contributed by EW last updated 2021-09-18 03:02:18 (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(R) message issued at 2021-09-18 02:58:34.6 UTC.

Earthquake

Title
M 4.4 - 0.8 mi SE of Carson
Time
2021-09-18 02:58:34.610 (UTC)
ShakeAlert Event ID
ew1631933910

Summary Report

ShakeAlert Messages Issued (after origin time):
Initial: 4.3 s
Final: 24.3 s
ShakeAlert System Magnitude Estimates:
Initial: M 4.7
Final: M 4.5
ANSS report: 128 s after origin, M4.4
ShakeAlert System Location Accuracy:
Initial: 1 km (1 mi) NNW
Final: 1 km (1 mi) NW
Wireless Emergency Alert:
WEA alerts are distributed to the MMI 4+ area if ShakeAlert Peak M >= 5.0
Number of Stations Reporting:
4 within 10km of epicenter
155 within 100km of epicenter
172 used in final ShakeAlert update
Nearby Cities
CityDistanceTime*Shaking (MMI**)
Carson 1 km (1 mi) ~0.0 s Moderate (V)
Long Beach 9 km (6 mi) — Weak (III)
Inglewood 17 km (11 mi) — Weak (III)
Los Angeles 25 km (16 mi) — Weak (III)

Radius shaken before Message release: 4 km (2 mi)

  • Marker
    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
    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.