Hector Quake - 7.1 Mw 10/16/99 2:46am PDT
October 17, 1999 - Keith and I met with Charles Watson out near the quake site. We were having an Aftershock Party, though only Keith actually felt one (2:08pm 2.6) !
Unfortunately, we couldn't get out to where all the action was. The quake occurred on the 29 Palm Marine Base - today they were having Live Ordinance excercises - so rather dangerous - we could have been shot, so we declined to get close up and personal with the fault scarps and rupture.
We did do some rather detailed inspections of the overpasses in the area, found lots of new cracks in the pillars and in the asphalt - also some offsets. There were some minor offsets in the road that runs alongside the highway - there was an area that was pretty well shattered - you could see evidence of boulders that were bounced, some pressure ridges.
We talked to some Caltrans guys inspecting the overpass with the most damage - the asphalt had been compressed together and they had scraped it flat again, a few bolts were sheared.
In inspecting some railroad tracks, we found up to 1/2 inch offset in the rails - actually pulled apart rather than offset - some of the railroad ties were skewed at an angle - railroad nails had popped out and such. We then went over and saw where the Amtrack train de-railed - they had replaced the rail and ties there - the train cars were off to the side of the road - 'TGI Friday's' lost some inventory !
We talked with Tom Rockwell, a professor of geology from UCSD that had flown over the area yesterday - he told us the offset was 4-5 meters and the rupture was 40 km long - It runs from Lavic Lake into the Bullion Mountains.
USGS is going back in 10/18/99 to do mapping of the area - apparently there are some nice fault scarps and such - there is a stream that was offset 12 ft. I have heard it was on the 'dormant' Lavic Lake Fault and stopped the rupture at the Bullion Fault. The faulting is right-lateral strike slip.
Additional Data Sources:
Some additional pictures taken by Paul "Kip" Otis-Diehl, USMC, 29 Palms are available at this link.
Southern California Earthquake Data Center information on The Hector Mine Earthquake.
For further information on the Hector earthquake and the Lavic Lake fault, see the U.S. Geological Survey Pasadena Office web site .
Commentary can be found at Trinet.
Charles Watson went back out on Monday and got some great Photos of the fault site.
|Heather (reporter for the Desert Sun) and Charles Watson, Geologist looking at map of area.||Damage to overpass pillar - small swiss army knife as size reference.|
|Under the overpass - cement sides on slope have been lifted.||Cracks in overpass.|
|Earth movement on slope.||Look at the discoloration - about 4 inches of earth settling on overpass.|
|Ron watching Charles - photographer for Desert Sun.||Charles looking at settling.|
|Movement at base of overpass pillar.||Offset on an empty Tank - see base has shifted.|
|Our tax dollars at work - Good job Guys! - This is the overpass with the most damage.||Some bolts have sheared off|