from California Geology, February 1979, Vol. 32, No. 2.

1857 EARTHQUAKE INTENSITIES NEAR LOS ANGELES, CALIFORNIA

Caltech News Release . . . .

SEE MAP

Earthquake intensities during the 1857 earthquake (M 8) plotted by Agnew and Sieh. Roman numerals indicate Modified Mercalli intensifies. Open circles represent locations with reported intensity, closed circles represent locations where earthquake was not felt. The extent of surface fault rupture along the San Andreas fault for the 1857 earthquake is shown. Map courtesy Bulletin of the Seismological Society of America.

The California earthquake of January 9, 1857, was one of the largest earthquakes to have happened in California in historical times (about the last 200 years). This event, which is estimated to have been about M 8 on the Richter scale, occurred along a segment of the San Andreas fault that extends from near Parkfield in central California to near San Bernardino. The earthquake was accompanied by surface fault rupture along this segment of the fault; strike slip displacements measured up to 9.5 meters in some locations. Ground motions during the event were variously reported as lasting from one to three minutes.

Kerry E. Sieh, Assistant Professor of Geology at the California Institute of Technology, and Duncan C. Agnew, graduate student at the Scripps Institution of Oceanography, have recently compiled reports of felt intensities of the 1857 earthquake from newspaper accounts, diaries, letters, and biographies. An intensity map of the 1857 earthquake was constructed from these accounts of the earthquake (figure 1).

Effect in Los Angeles Area

The intensity of the earthquake within what is now metropolitan Los Angeles was not extremely high, despite heavy shaking in the vicinity of the fault. None of the adobe structures within the Los Angeles area sustained any great damage, although some structures in the San

Fernando Valley were destroyed. This fact suggests that, were the 1857 earthquake to be repeated today, there would not be extensive damage to low-rise construction in the metropolitan Los Angeles area. However, there probably would be substantial damage to such structures located along the fault.

Evidence indicated that the 1857 earthquake was associated with substantial, low-frequency, long-period waves. If the same earthquake were to occur today, these low-frequency, long-period ground motions would have the greatest impact on large structures. The severity of their effect on large structures could not be extrapolated from the 1857 earthquake accounts.

Foreshocks

Numerous foreshocks occurred during the several hours preceding the main shock. From historical accounts, the epicenters of the foreshocks were located in central California near the northwestern extent of the main shock fault rupture.

Epicenters of the last two foreshocks, which were estimated to be between M 5-6, were located within a 60 kilometer radius of a segment of the San Andreas fault that has historically be characterized by creep. The relatively constant slippage along this segment of the fault relieves much of the strain, but the reach of the San Andreas fault from about Parkfield to San Bernardino is locked and thus not continually relieved. Stresses within this central segment of the fault continually build and every few hundred years become so great that the locked section ruptures suddenly and a great earthquake similar to that of 1857 occurs.

The foreshocks in the creeping segment may have triggered the main shock. Therefore, it appears that the 1857 earthquake occurred by propagating from the northwesterly creeping segment of the fault southeastward into and through the locked segment. If the 1857 earthquake did occur in this fashion, it implies that studies of the creeping segment of the San Andreas fault north of Parkfield may aid in predicting the next great 1857-type earthquake in southern California.

The following historical accounts illustrate the intensity of ground motions at various locations in California during the 1857 earthquake and individual reactions to the shaking.

Fort Tejon

"The main disturbing force of the shocks which were so widely felt on the 9th, without doubt, was in the vicinity of the Fort [Fort Tejon], and extended to an unknown distance in the Desert. The earthquake occurred on Friday morning, the 9th instant, at about the same time that it was felt here [Santa Barbara]. All the houses, with two exceptions, were thrown down or otherwise injured so as to be rendered entirely useless. The shock was preceded with a peculiar rushing or rumbling noise, and for more than a week thereafter noises somewhat resembling distant thunder were heard. Fortunately, no serious damage to life or limb occurred. Mrs. Kirkham, wife of the Quartermaster, was slightly injured. Immediately after the shock had passed, an express messenger with advises was dispatched to General Wool. All of the public works at the Fort are necessarily suspended. The damages are estimated at $50.000.

"At the 'Mill,' some twelve miles west of Tejon, the shock was very heavy. It tore up large trees and twisted off branches, threw people on the ground, and when over, caused a general stampede for the Fort, upon the supposition, we suppose, that that place was 'safe as any.' and that 'misery loves company.' One mile and a half this side [southwest] of the Fort a lady was badly hurt. When the shock was first felt, she ran out of the house and crept under a cart for safety. A limb of a tree standing close by, fell down directly across the cart, which it crushed to pieces, injuring her severely. Mr. Gale, whose dwelling was situated about the same distance from the Fort, experienced a severe injury during his exertions to rescue his children from the ruins of his falling house. At Reed's Rancho, six miles from Tejon on the Los Angeles trail, the wife of Mr. Reed's vaquero was killed. A beam fell in the house on her head, killing her instantly. "A large rent in the earth was traced by Mr. Warner a distance of eight leagues [about 40 kilometers]. When on the high ground by Elizabeth Lake it could still be discerned running in an easterly direction towards the Colorado river. This rent was in some places five to 10 yards wide, the earth at times filling it up like ploughed furrows; at others the ground stood apart, leaving a deep fissure. Its course was in a straight direction, across valleys, through lakes and over hills, without regard to inequality or condition of surface. On either side, the ground had been more or less disturbed for a long distance."

Account by Mr. Warner, published in the Santa Barbara Gazette, January 22, 1857

Los Angeles

"In another instant, the fearful cry of 'earthquake' issued from every mouth---then a rush, shouting and screaming, such as may well be conceived, but cannot be described. At the hotels, the breakfast tables were instantly deserted; people wildly rushed to the streets, tripping and tumbling over each other in their hurry and dismay---in some cases, blocking up the door, so as to prevent egress for the moment. Many, used to indulge in a comfortable snooze on a morning, were unceremoniously turned out of their comfortable quarters, in anticipation of having the roof about their ears before they could make their exit. These took no thought of their toilet---but gallantly gave their linen to the breeze, in hopes of bringing up in safe quarters. One gentleman, who, in his hurry, mistook his window for a door. was seen running along the roof of an adobe building, thinking, should it fall, it was better to be on top of it, than it on top of him. Another, enjoying the luxury of a bath, stood the rocking for some time, but at last was compelled to evacuate the premises, and rush to the yard, where to his horror a number of ladies had also sought refuge and were seeking consolation in prayer. Whether from the shock to his feelings, or the shock of the earthquake, he was immediately brought prone to the earth, when he managed to creep under cover, unobserved. . . ."

Los Angeles Star, January 17, 1857

San Bernardino

"One pleasant morning I was searching through garden paths for roses I heard a far off smothered, rumbling sound, that I scarcely noticed, for I thought I was growing dizzy, and not understanding why I should feel so, I started for the house. As I stepped across a narrow stream, the opposite bank seemed first to recede from me, then instantly to heave upward against my feet. As this threw me from my equilibrium, the water emptied out on either bank, and hearing an Indian's voice in loud supplication. I turned and saw our Lothario on his knees, the ground rising and falling in billows around him. At the same instant I saw my parents and sisters clinging to large trees, whose branches lashed the ground, birds flew irregularly through the air shrieking, horses screamed, cattle fell bellowing on their knees, even the domestic feathered tribe were filled with consternation. Voices of all creatures, the rattling of household articles, the cracking of boards, the falling of bricks, the splashing of water in wells, the falling of rocks in the mountains and the artillery-like voice of the earthquake, and even that awful sound of the earth rending open---all at once, all within a few seconds, with the skies darkened and the earth rising and falling beneath the feet---were the work of an earthquake. It passed---we rejoined each other, thankful that life was spared, and looked around with trembling. upon the scene, where utmost terror had reigned."

Reminiscence by Augusta J. Crocheron, 1885