Mag 7.0 - Offshore Cape Mendocino, California, 5 Dec, 2024

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Discussion Overview

The discussion centers around the magnitude 7.0 earthquake that occurred offshore Cape Mendocino, California, on December 5, 2024. Participants discuss the earthquake's characteristics, including its depth, location, and the subsequent tsunami warning issued for Northern California. The conversation also touches on aftershocks and the geological context of the event.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants note the earthquake's location at the junction of the Gorda, Juan de Fuca, and Pacific plates, highlighting the tectonic complexity of the region.
  • Others report on the tsunami warning issued for coastal Northern California and the rapid dissemination of alerts via social media.
  • A participant mentions the cancellation of the tsunami alert shortly after it was issued.
  • One participant challenges the characterization of the fault mechanism, asserting it is a strike-slip fault rather than a subduction zone event.
  • Another participant provides information about the aftershocks, noting that there have been 120 small quakes ranging from magnitude 2.5 to 4.2 following the main event.

Areas of Agreement / Disagreement

Participants generally agree on the occurrence of the earthquake and the issuance of the tsunami warning. However, there is disagreement regarding the fault mechanism involved, with some asserting a strike-slip nature while others may hold different views.

Contextual Notes

There are unresolved aspects regarding the specific fault mechanics and the implications of the aftershocks, as well as the potential for future seismic activity in the region.

Astronuc
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M 7.0 - 2024 Offshore Cape Mendocino, California Earthquake
https://earthquake.usgs.gov/earthquakes/eventpage/nc75095651/executive
  • 2024-12-05 18:44:19 (UTC)
  • 40.370°N 125.025°W
  • 0.6 km depth
Tsunami warning for coastal N. California.

Quake and after shocks at the junction of the Gorda plate (south of Juan de Fuca plate), Pacific plate and N. American Plate.
https://en.wikipedia.org/wiki/Gorda_plate
https://en.wikipedia.org/wiki/Juan_de_Fuca_plate
http://www.usarray.org/researchers/obs/cascadia
 

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Astronuc said:
Tsunami warning for coastal N. California.
Yeah, I got a very loud alarm notification on my cellphone for that. Word spread pretty quickly on social media, and I think most folks in Santa Cruz (to the west of Silicon Valley) were notified to stay away from the water. The alert just got cancelled a few minutes ago.
 
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Astronuc said:
Tsunami warning for coastal N. California.

berkeman said:
The alert just got cancelled a few minutes ago.

Yup, completely the wrong type of fault mechanism -- strike-slip instead of subduction

here's my seismogram of the event

241205 1844UT M7.0 offshr Cape Mendicino, nthrn Calif zhi.gif
 
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So far, 120 small quakes (aftershocks of Mag 2.5 to 4.2) off-shore following the Mag 7 earthquake. There are three small earthquakes in California.
 

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