Pasadena’s shaky state

Of­fi­cials remap the Ray­mond fault, which poses a big quake risk in the metro area.

Los Angeles Times - - CALIFORNIA - RONG-GONG LIN II ron.lin@la­times.com

Cal­i­for­nia of­fi­cials have mapped a new stretch of an earth­quake fault through north­east Los Angeles — a fault that could cause ma­jor dam­age in the heart of the metro area.

The Ray­mond fault has long been known as a po­ten­tially dan­ger­ous fault for Los Angeles and the San Gabriel Val­ley, and caused the mag­ni­tude 4.9 Pasadena earth­quake in 1988, said Tim Daw­son, se­nior en­gi­neer­ing ge­ol­o­gist for the Cal­i­for­nia Ge­o­log­i­cal Sur­vey.

It’s a fault that can pack a punch. That 1988 earth­quake lit­er­ally threw seis­mol­o­gist Lucy Jones out of bed. “The wave was com­ing up at me,” Jones re­cently re­called. “It was the most scared I have been in earth­quake shak­ing.”

And it’s ca­pa­ble of a much worse earth­quake. It could cause an earth­quake as large as mag­ni­tude 7. The Ray­mond fault runs from north­east L.A. through South Pasadena, Pasadena, San Marino, the un­in­cor­po­rated area of East Pasadena, Ar­ca­dia and Mon­rovia. For stretches, the fault runs along­side parts of Ea­gle Rock, York and Hunt­ing­ton boule­vards and un­der a por­tion of the 110 Free­way in South Pasadena.

A known haz­ard

Earth­quake faults are gi­ant cracks in Earth’s sur­face, bound­ary lines of sorts be­tween shift­ing tec­tonic plates. When a ma­jor earth­quake hits a fault like the Ray­mond, the plates sud­denly move in op­po­site di­rec­tions along the path of the fault.

The Ray­mond fault has long been known to ex­perts, and much of the fault was mapped in the 1970s by the state. The Cal­i­for­nia Ge­o­log­i­cal Sur­vey is­sued a re­vised map of it last week.

The most sig­nif­i­cant changes in­volved ex­tend­ing the fault to the west, adding ar­eas of Glas­sell Park, Ea­gle Rock and High­land Park to the fault zone. The fault zone was also moved far­ther south in High­land Park.

In the San Gabriel Val­ley, changes to the so-called Alquist-Pri­olo earth­quake fault zone were mi­nor.

Any­one seek­ing to build a struc­ture for hu­man oc­cu­pancy in a fault zone is re­quired to con­duct test­ing to de­ter­mine whether the build­ing would be di­rectly on top of a fault.

State law gen­er­ally bans such con­struc­tion.

A big earth­quake on the Ray­mond fault could pro­duce cat­a­strophic dam­age lo­cally. It’s also pos­si­ble that it could rup­ture al­most si­mul­ta­ne­ously with the Hol­ly­wood fault.

“This is a fault right in the ur­ban area,” Daw­son said. “It is an ac­tive fault. There are a lot of build­ings in close prox­im­ity of the fault.”

Vul­ner­a­ble com­mu­ni­ties

Los Angeles has taken steps to re­duce the threat of ma­jor earth­quakes; city lead­ers in 1981 or­dered that brick build­ings be retro­fit­ted or de­mol­ished and in 2015 passed a law re­quir­ing vul­ner­a­ble wood apart­ments and con­crete build­ings to be retro­fit­ted. Suburbs are far be­hind. South Pasadena only re­cently de­cided to take a new look at brick build­ings and found out that nearly half of the 60 brick struc­tures — in­clud­ing stores, restau­rants, apart­ments and churches — in that city were not retro­fit­ted. Last year, the City Coun­cil re­quired the rest of them to be fixed, giv­ing own­ers a dead­line of 2½ years to com­ply once they re­ceive a new or­der to do so.

Also a prob­lem: Apart from L.A., Santa Mon­ica and West Hol­ly­wood, most L.A. County cities have not man­dated retrofitting of wooden apart­ment build­ings with flimsy ground floors that serve as car­ports or garages. Such vul­ner­a­ble apart­ments are com­mon across the re­gion on top of the fault, like in South Pasadena, and near the fault, such as in Al­ham­bra.

Six­teen peo­ple died in the col­lapse of such an apart­ment build­ing dur­ing the mag­ni­tude 6.7 Northridge earth­quake in 1994.

Cre­at­ing lakes and hills

Ev­i­dence for the fault has been clear to ge­ol­o­gists for decades. A lake that once sat at what is now Lacy Park in San Marino was cre­ated by the fault, a re­sult of land sink­ing from past earth­quakes, Daw­son said.

The earth­quakes also cre­ated the hills that are now part of the L.A. County Arboretum & Botanic Gar­den in Ar­ca­dia, and those that give the com­mand­ing views at the Hunt­ing­ton Li­brary, home to a his­toric es­tate, li­brary, art col­lec­tion and gar­dens es­tab­lished by rail­way mag­nate Henry Hunt­ing­ton.

“The Hunt­ing­ton Li­brary sits on the up-thrown side of the Ray­mond fault. When the Hunt­ing­tons moved there, they moved there be­cause it had a nice view — that view was cre­ated by the fault,” Daw­son said. “Over many earth­quakes, that hill has gone up.”

A slow-mov­ing fault

Com­pared with the fastest-mov­ing faults in the state, the Ray­mond fault moves slowly — at about one-10th the speed of the in­fa­mous San An­dreas fault, Daw­son said.

That means that the Ray­mond fault doesn’t rup­ture as of­ten as the San An­dreas, a stretch of which north of L.A. is be­lieved to experience a big quake every 100 years on av­er­age. That sec­tion of the fault last caused a mag­ni­tude 7.9 earth­quake in 1857.

Sci­en­tists sus­pect the last time the Ray­mond fault pro­duced an earth­quake of mag­ni­tude 6 or above was 1,000 to 2,000 years ago. They be­lieve that such events hap­pen every few thou­sand years on av­er­age.

But earth­quakes don’t hap­pen like clock­work, and sci­en­tists can­not say for cer­tain when the Ray­mond fault will rup­ture next.

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