M 4.5 - 3km WSW of South El Monte, CA

  • 2020-09-19 06:38:46 (UTC)
  • 34.038°N 118.080°W
  • 16.9 km depth

ShakeAlert ®

 Contributed by EW last updated 2020-09-19 06:44:45 (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 2020-09-19 06:38:46.9 UTC.

Earthquake

Title
M 4.6 - 2.0 mi W of South El Monte
Time
2020-09-19 06:38:46.940 (UTC)
ShakeAlert Event ID
ew1600497528

Summary Report

ShakeAlert Messages Issued (after origin time):
Initial: 4.7 s
Final: 12.6 s
ShakeAlert System Magnitude Estimates:
Initial: M 4.5
Final: M 4.8
ANSS report: 131 s after origin, M4.6
ShakeAlert System Location Accuracy:
Initial: 2 km (1 mi) N
Final: 1 km (1 mi) NNW
Wireless Emergency Alert:
WEA alerts are distributed to the MMI 4+ area if ShakeAlert Peak M >= 5.0
Number of Stations Reporting:
5 within 10km of epicenter
167 within 100km of epicenter
99 used in final ShakeAlert update
Nearby Cities
CityDistanceTime*Shaking (MMI**)
South El Monte 3 km (2 mi) ~0.4 s Moderate (V)
East Lost Angeles 8 km (5 mi) ~0.8 s Light (IV)
Pasadena 13 km (8 mi) ~1.5 s Light (IV)
Los Angeles 15 km (9 mi) ~1.9 s Light (IV)
  • Marker
    50 km
    30 mi
    Figure 1. ShakeAlert initial earthquake location (black dot). Star is regional network epicenter. Polygon is the predicted outer range for felt ground motion (MMI 2). Red circle is front of peak shaking when the alert was released. Shaking takes 10 s to expand from circle to circle.
  • Marker
    50 km
    30 mi
    Figure 2. Polygons show shaking intensity contours for the peak magnitude ShakeAlert. Shaking of intensity 3 or less is often not felt. Star shows the regional network 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.