Moderate mag. 3.9 earthquake - 28 mi north of Ukiah, Mendocino County, California, USA, on 23 Apr 4:18 am (GMT -7) -
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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Date & time: 23 Apr 2021 11:18:40 UTC -
Local time at epicenter:
23 Apr 4:18 am (GMT -7)
Depth: 7.4 km
Epicenter latitude / longitude: 39.52567°N / 123.0365°W
, United States
Nearest volcano: Clear Lake
(66 km / 41 mi)
Nearby towns and cities:24 km (15 mi) NNE of Potter Valley
(pop: 646) --> See nearby quakes!30 km (19 mi) ENE of Willits
(pop: 4,860) --> See nearby quakes!32 km (20 mi) NNE of Redwood Valley
(pop: 1,730) --> See nearby quakes!35 km (22 mi) SSE of Covelo
(pop: 1,260) --> See nearby quakes!42 km (26 mi) ESE of Laytonville
(pop: 1,230) --> See nearby quakes!44 km (28 mi) NNE of Ukiah
(pop: 15,900) --> See nearby quakes!50 km (31 mi) NNW of North Lakeport
(pop: 3,310) --> See nearby quakes!72 km (45 mi) NNW of Clearlake (Lake County)
(pop: 15,200) --> See nearby quakes!124 km (77 mi) NNW of Santa Rosa
(pop: 175,000) --> See nearby quakes!170 km (105 mi) NW of Sacramento
(pop: 490,700) --> See nearby quakes!
Weather at epicenter at time of quake:
Broken Clouds 5.9°C
(43 F), humidity: 81%, wind: 2 m/s (3 kts) from NE
Primary data source: USGS
(United States Geological Survey)
Estimated released energy: 4.5 x 1010
joules (12.4 megawatt hours, equivalent to 10.7 tons of TNT) More info
Data for the same earthquake reported by different agencies
Info: The more agencies report about the same quake and post similar data, the more confidence you can have in the data. It takes normally up to a few hours until earthquake parameters are calculated with near-optimum precision.
|3.9||7.4 km||15km NNW of Lake Pillsbury, CA, USA||USGS|
|3.4||5 km||NORTHERN CALIFORNIA, USA||EMSC|
User reports for this quake (6)
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San Jose, California 95148 / Light shaking (MMI IV) / single lateral shake / 2-5 s : Woke me up from sleep, a bag of items on top of another bag of items fell over. Then the wall behind me seemed to be jolted once northeasterly, creaked, rumbled and stopped. From jolt to stop was 2 seconds tops.
Orange, CA / Light shaking (MMI IV) / single lateral shake / 5-10 s
Nas Lemoore (455.8 km SE of epicenter) [Map] / Very weak shaking (MMI II) / horizontal (sideways) swinging / 5-10 s
San Jose / Very weak shaking (MMI II) / single vertical bump / 1-2 s
5726 Ridgewood Road Willits, CA (27.6 km SW of epicenter) [Map] / Light shaking (MMI IV) / horizontal (sideways) swinging / 2-5 s : Woke up to house shaking.
93041 / Light shaking (MMI IV) / rattling, vibrating / 2-5 s
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