Earthquake swarm in NW Arizona up to 42 events, largest is magnitude 3.7

AZGS put out a news release today on the earthquake swarm in northwest Arizona that reported 42 earthquakes have been detected since March 28.  That was out of date very quickly. There was another event just before midnight on the 18th (ML=1.3) and a ML=2.3 just after noon today.  Our colleagues at the Nevada Seismic Laboratory who are providing key data on earthquake locations say this appears to be an unusual event, rather than something that happens regularly but just had not been detected before.  They indicate the instrument network should have been able to detect such events for the past couple of years at least.

Here is the AZGS release from earlier today:

A magnitude (ML) 3.7 earthquake shook northwestern Arizona south of Littlefield, Arizona, at 9:06 pm on 17 April 2016. This event is part of a swarm of more than 42 small magnitude earthquakes that began on 28 March with an ML > 2.1 event located approximately 29 miles SSE of Littlefield, Arizona. The most recent event, ML 1.3, occurred at 4:58 pm (MST) on 18 April.

The ML 3.7 event was the largest earthquake yet and was felt in Littlefield and Mesquite, Nevada, along the remote Arizona-Nevada border. The earthquake sequence includes 2 events >ML 3.0, 8 events >ML 2.0 with the remainder below ML 2.0. The depths of the earthquakes range from near-surface to approximately 14 km.

The earthquake swarm is situated along the physiographic boundary between the Colorado Plateau and the Basin and Range Province, an area of active crustal extension and seismicity.

We anticipate additional small magnitude aftershocks in the wake of the ML 3.7 event.

This apparent increase in earthquake activity of northwestern Arizona may be the result of efforts by the Nevada Seismological Laboratory (NSL) to capture and record small magnitude events along the Nevada-Arizona border. The Arizona Geological Survey’s broadband seismic network, comprising 8 seismometers, is unable to record small magnitude events in northwestern Arizona.

AZGS operates the seismic network without any state or federal funding so continues to look for ways to maintain the system and to increase statewide coverage of currently undetected earthquakes.

For additional information on the more than 3,000 historical earthquakes and active faults in Arizona, see the Natural Hazard in Arizona Viewer. 

Below is the list of the first 40 earthquakes recorded in the swarm.  We are continually updating it with new events.

No.	DATE	ML	LAT	LONG	Depth (km)
1	4/18/2016	2.1	36.4730	-113.9650	0
2	4/18/2016	1.6	36.4920	-113.9950	1.2
3	4/17/2016	0.9	36.4870	-113.8830	0
4	4/17/2016	1.3	36.5020	-114.0000	8.2
5	4/17/2016	1	36.4970	-114.0040	0
6	4/17/2016	1.6	36.4930	-113.9890	0
7	4/17/2016	1.7	36.4800	-113.9920	2.4
8	4/17/2016	2.3	36.4820	-113.9830	2.1
9	4/17/2016	1.8	36.4710	-113.9710	0
10	4/17/2016	3.7	36.4720	-113.9740	4.8
11	4/15/2016	2	36.8670	-113.4470	13.7
12	4/14/2016	1.3	36.5050	-114.0090	6.6
13	4/11/2016	0.6	36.5020	-113.9310	0
14	4/11/2016	0.6	36.5540	-113.9200	8.3
15	4/9/2016	0.4	36.5340	-113.9680	8.7
16	4/9/2016	0.6	36.4990	-114.2000	7.2
17	4/9/2016	0.9	36.4880	-114.0050	0.5
18	4/8/2016	3.4	36.4975	-113.4372	22
19	4/7/2016	2.7	36.4860	-113.9970	7.8
20	4/6/2016	2.4	36.4950	-114.0070	7.9
21	4/4/2016	1	36.4890	-113.9890	6.3
22	4/3/2016	1.1	36.5140	-114.0240	0
23	4/3/2016	2.6	36.4560	-113.9790	6.1
24	4/3/2016	0.7	36.5210	-114.0310	0
25	4/3/2016	1.1	36.4810	-113.9710	0
26	4/3/2016	1.1	36.4890	-113.9710	10.9
27	4/3/2016	1	36.4890	-113.9890	6.3
28	4/2/2016	1.2	36.4880	-113.9870	10.5
29	4/2/2016	1	36.4730	-113.9790	10.7
30	4/2/2016	1.7	36.4920	-113.9980	5.8
31	4/1/2016	1.5	36.4930	-114.0020	9.8
32	4/1/2016	2	36.4980	-113.9920	0
33	3/31/2016	1.6	36.4860	-113.9220	3.1
34	3/30/2016	1	36.5240	-114.0140	8.8
35	3/30/2016	1.7	36.4390	-113.9690	0
36	3/29/2016	1.6	36.5060	-114.0040	0.9
37	3/29/2016	1.8	34.4950	-113.9800	13.2
38	3/29/2016	0.8	36.4830	-114.0040	3.8
39	3/29/2016	2.3	36.5400	-114.0130	15
40	3/28/2016	2.1	36.5380	-114.0110	0