Moderate magnitude 3.9 earthquake at 7 km depth
23 Apr 11:22 UTC: First to report: USGS after 4 minutes.
23 Apr 11:24: Magnitude recalculated from 3.7 to 4.0.
23 Apr 14:02: Magnitude recalculated from 4.0 to 3.9.
23 Apr 18:00: Hypocenter depth recalculated from 6.6 to 7.4 km (from 4.1 to 4.6 mi).
Update Fri, 23 Apr 2021, 11:27Moderate magnitude 4.0 quake hits 28 miles northeast of Ukiah, California, United States early morning
4.0 quake 23 Apr 4:18 am (GMT -7)
The United States Geological Survey reported a magnitude 4.0 quake in the United States near Ukiah, Mendocino County, California, only 8 minutes ago. The earthquake hit early morning on Friday 23 April 2021 at 4:18 am local time at a very shallow depth of 4.1 miles. The exact magnitude, epicenter, and depth of the quake might be revised within the next few hours or minutes as seismologists review data and refine their calculations, or as other agencies issue their report.
Our monitoring service identified a second report from the European-Mediterranean Seismological Centre (EMSC) which listed the quake at magnitude 4.0 as well.
Based on the preliminary seismic data, the quake should not have caused any significant damage, but was probably felt by many people as light vibration in the area of the epicenter.
Weak shaking might have been felt in Potter Valley (pop. 650) located 15 miles from the epicenter, Willits (pop. 4,900) 19 miles away, Brooktrails (pop. 3,200) 19 miles away, and Redwood Valley (pop. 1,700) 20 miles away.
Other towns or cities near the epicenter where the quake might have been felt as very weak shaking include Covelo (pop. 1,300) located 22 miles from the epicenter, Ukiah (pop. 15,900) 28 miles away, Nice (pop. 2,700) 30 miles away, and Clearlake (pop. 15,200) 45 miles away.
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