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Location:
21km NNE of Trona, CA
Period:
28 Sep 2002 10:34:47 - 30 Sep 2002 08:18:57 (1 day 21 hours 44 minutes)
Volcanoes in 100km radius:
None
Earthquakes:
48
10 swarms found nearby.
2008
S20080510.1(27.6km)
9 May
2 days 4 hours
47 earthquakes
29 Nov
16 days 16 hours
369 earthquakes
2014
4 Mar
4 days 14 hours
79 earthquakes
2019
S20190705.2(10.1km)
4 Jul
29 days 2 hours
2446 earthquakes
5 Jul
39 days 7 hours
2694 earthquakes
5 Jul
12 days 17 hours
712 earthquakes
6 Jul
8 days 16 hours
302 earthquakes
S20190708.2(15.2km)
7 Jul
4 days 17 hours
70 earthquakes
2020
23 Mar
4 days 2 hours
52 earthquakes
S20201030.1(28.6km)
29 Oct
2 days 2 hours
54 earthquakes
AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Seismic Swarm S20020928.1 Near Trona, California

A notable earthquake swarm, designated S20020928.1, occurred 21 km north-northeast of Trona in San Bernardino County, California. The sequence began at 10:34 on 28 September 2002 and concluded at 08:18 on 30 September 2002, spanning 45 hours and 44 minutes. During this interval, 48 earthquakes were recorded, with magnitudes ranging from 1.0 to 4.1 and focal depths primarily between 0 and 6 km.

The swarm initiated with a magnitude 4.1 event at 2 km depth, followed rapidly by smaller shocks. Activity intensified later on 28 September, including a pair of events with magnitudes 3.9 and 3.7, both at 2 km depth. Subsequent events remained predominantly shallow, with several registering at depths of 3–6 km. A single event was noted at a reported depth of -1 km, consistent with internal catalog classification. The sequence tapered off with lower-magnitude events through 29 September before ending on 30 September.

The Trona region lies within the Mojave Desert portion of the Eastern California Shear Zone, an area of distributed right-lateral shear accommodating Pacific–North American plate motion. Local geology features Quaternary alluvium overlying older sedimentary and volcanic units around Searles Lake, with active faulting influenced by the nearby Garlock Fault system and subsidiary northwest-trending structures. Historical seismicity in the broader area includes both isolated events and episodic swarms, reflecting the region’s transtensional regime.

Analysis of the 2002 swarm indicates a clustered, non-mainshock-aftershock pattern typical of fluid-related or aseismic-slip-triggered sequences common in this tectonic setting. Magnitudes were modest, with only three events exceeding magnitude 3.0, and the majority clustered in the first 12 hours. Depths concentrated in the upper crust suggest activation of shallow fault segments or fracture networks.

SeismoSight internal records provide the complete event list used for this summary. Additional context draws from regional tectonic frameworks documented by the U.S. Geological Survey and the Southern California Earthquake Data Center.