CITYWIDE — There’s been a lot of rumblings about fault lines in Santa Monica recently.
The Los Angeles Times identified four Santa Monica buildings that may sit on top of a fault. City officials responded, saying they are confident that the buildings are located near but not on the fault.
State Sen. Ted Lieu (D-Santa Monica) sent a letter to State Senate leader Darrell Steinberg, asking for more cash to be allocated for fault mapping.
The Alquist-Priolo Earthquake Fault Zones, created by the California Geological Survey (CGS), allow the state to regulate development built near faults. Santa Monica does not yet have one of these zones but it likely will by the end of the year.
The Daily Press spoke with California State Geologist John Parrish, who will be a part of the team that tackles the Santa Monica Fault later this year.
Daily Press: What is the CGS working on now?
John Parrish: We’re finishing up the Hollywood Fault zone. That should be out, the preliminary release, in the first part of January. After we’ve finished that, we’re going to start working off the Santa Monica Fault. That could take six to eight months.
DP: How does that zone restrict development?
JP: They can build in the zone so long as they’re not on top of one of the traces of the fault. That zone we put around it is because we think there are a number of traces in there that need to be better defined. They can only be defined by a very, very thorough examination of that particular building site. That gets down to parcels of land and we don’t get down that specific.
DP: What happens if developers find a fault?
JP: The (Alquist-Priolo Act) says that you don’t build a structure for human habitation across the surface rupture of a fault. When that fault moves the next time it’s going to rupture on the surface and it will tear the foundations out from underneath the building. No matter how strong you think you build, the foundations are ripped in opposite directions. The building is going to be worthless and cause possible catastrophic damage to the area. They want you to set off of the surface trace, not astride it.
DP: Why update the current CGS maps?
JP: The current map is actually a statewide map done on a statewide scale. So, a difference of 3 millimeters on the map is a difference of about 1 kilometer on the ground.
DP: Will the new map identify the fault line in Santa Monica?
JP: We map it on a very close scale so we get it down to within just a few feet of where it really is. When we put a zone on that, it becomes a zone of mandatory investigation. Anybody who wants to develop in that zone must narrow it down even further by pinning down the exact location of where that surface fault is.
DP: What’s the mapping process like?
JP: It’s a long process. We look at all the different mappings that have been done on that fault from the 1800s through the present. We looked at our own mapping and then we take the best of everything, including doing a little field work out there. When we’re satisfied and we think we have the best handle on it, we justify that with lots of reports and data. We will then draw a zone, which encompasses about 500 to 1,000 feet on either side of the fault.
DP: In the past, have you found that these zones slow or halt development?
JP: We did a study several years ago on the effects of the Alquist-Priolo zones and we found that it was really very well received and it did not form a hindrance to local development. It’s because you generally know where it is. It’s a relatively narrow zone, 1,000 feet wide. A lot of times you can put a street on that or park lands or something along those lines so it did not hinder it too much.
DP: You haven’t started mapping the Santa Monica Fault yet, but do you have any preconceived notions about it?
JP: Yes, it’s a segment of about a 200-mile long fault and the Hollywood Fault is a segment of this same system. Santa Monica Fault is the same as the Malibu Fault. These are all segments of a much longer fault.
DP: Is the activity of this fault important?
JP: Absolutely. In fact, it has to be an active fault before we’ll actually put a zone around it. That activity is defined by the State Mining and Geology Board as any fault that has moved in the last 11,000 years. People sort of get chagrined at that, but actually there are pieces in the fault that have moved within the last 1,000 years that are maybe due again, we don’t know. Sometimes faults move within several hundred years. We have a pretty good handle on the Santa Monica Fault. It’s active and we have a fair handle on where it is.
DP: Being that the Hollywood Fault is on the same fault system, does the activity of the Hollywood Fault say anything about the activity of the Santa Monica Fault?
JP: They’re all joined together and activity on any one part will influence the other parts.
DP: So how active are you finding the Hollywood part?
JP: There was some work on the fault that was around the Veteran’s Hospital out there and they found that moved around 1,400 years ago. We’ve seen some younger areas in outcrops so we still have to work on those.
DP: How active is that considered?
JP: That’s considered pretty active but a number of these faults move every several hundred years and the San Andreas maybe every 150 years. Some of these are every 300 years, 500 years, but if one fault moves it can trigger other faults to go.
DP: How do you decide what to map next?
JP: It’s been, of course, very slow because of budgetary concerns. We have mapped about 5,000 miles of surface faults put in the Alquist-Priolo zones. It forms less than 1/10 of one percent of the area of California so it doesn’t really take up a lot of space, and we did that with about 550 maps. You probably have another 2,000 miles left to map and what we’re trying to do is find funding. It’s a legislatively mandated program but not a legislatively funded program so it’s slow going for right now. That’s why we’re probably doing about one fault zone a year; it’s the best we can muster. And Santa Monica’s next on our list.