  Las Vegas Santa Barbara San Diego  | |
| UTC time | 1990-02-28 23:43:36 |
|---|---|
| ISC event | 380064 |
| USGS-ANSS | ComCat |
| Local date | February 28, 1990 |
| Local time | 23:43:37 UTC[1] |
| Magnitude | 5.7Mw[1] |
| Depth | 10 km (6.2 mi)[1] |
| Epicenter | 34°10′N117°44′W / 34.16°N 117.73°W /34.16; -117.73[1] |
| Fault | San Jose Fault |
| Type | Strike-slip[2] |
| Areas affected | Greater Los Angeles Area Southern California United States |
| Total damage | $12.7 million[2] |
| Max. intensity | MMI VII (Very strong)[3] |
| Peak acceleration | 1.05g[4] |
| Casualties | 30 injured[2] |
The1990 Upland earthquake occurred at15:43:37 local time on February 28 with amoment magnitude of 5.7 and a maximumMercalli Intensity of VII (Very strong). This left-lateral strike-slip earthquake occurred west of the San Andreas Fault System and injured thirty people, with total losses of$12.7 million. Many strong motion instruments captured the event, with an unexpectedly high value seen on water tank near the epicentral area.
In theTransverse Ranges west of the right-lateralSan Andreas Fault System, some faults exhibit left-lateral slip, including some at the boundary of theLos Angeles Basin and the Transverse Ranges.[5]
While several examinations of earthquake focal mechanisms in the Upland area showed both thrust and strike-slip faulting on opposite ends of the San Jose Fault, the mechanism of the 1990 event showed pure left-lateral motion on a steeply-dipping (70°) and northeast-striking fault. Field investigations revealed that the bilateral rupture did not reach the surface.[6]
The shock was felt fromSanta Barbara in the west and toLas Vegas in the east. It was also felt inEnsenada, Baja California and it triggered 82 strong motion instruments at distances of 3–76 kilometers (1.9–47.2 mi). Typical ground accelerations were around 0.1g at distances of up to 30 km (19 mi), but some closer stations had significantly higher responses.[4]
Rockslides left some roads closed in theSan Gabriel Mountains and Pomona city hall was heavily damaged. InClaremont some buildings were damaged, but only one building in Upland's historic downtown area was tagged for non-occupation. Those that were injured suffered cuts and bruises (mainly from falling objects) but two men were injured as a result of a landslide.[7][8]
