19: California's Earthquake History and Hazards

Introduction: A Noble Quake

The high desert is cold at night. At half past two in the morning, the fierce daylight winds have settled, and the coarse desert sands take their rest, along with dreamers snoring in their beds. Far, far above them all, the Milky Way galaxy–bright and sharp in the clear night–slowly plows across the dark expanse of sky. The universe itself seems quiet.

And then the sound. Rocks grind and crack. Tin water pails clang to the floor and splash. Adobe brick walls grind and teeter and fall, thumping to the ground. A deep grumble, like the yawn of an awakening dragon, fills the air, startling jackrabbits who sprint from an unseen enemy, panicked birds clapping their wings as they escape to the sky. But on the ground, the pain has just begun.

Two hundred kilometers away, naturalist John Muir springs from his cabin with joy as he hears boulders cascade down the vertiginous cliffs of Yosemite. One can learn that a volcano is erupting and consciously decide to visit it, but to experience an earthquake–a noble earthquake!--one must be in just the right confluence of time and place when a temblor occurs. John Muir has never felt an earthquake before and he is excited.

Back in the tiny mining camp of Lone Pine, his enthusiasm was not shared. Of the 59 houses in Lone Pine, 52 collapsed. Of the 250-300 residents of Lone Pine, 27 died in this quake.

Let’s consider these numbers. San Francisco currently has over 400,000 housing units, ranging from single family homes to large apartment complexes. In the 1872 Lone Pine quake, 52 of the 59 homes were destroyed–a loss rate of 88%. If a comparable quake today destroyed 88% of San Francisco’s housing units, that would be over 350,000 homes lost.

Lone Pine had somewhere between 250 to 300 residents and 27 were killed. If we round the population to 270, then the loss of 27 is a 10% death rate. San Francisco currently has about 815,000 residents. If the 1872 Lone Pine death rate applied to a San Francisco quake, about 81,500 people would be killed. This would far exceed the combined death tolls from all the worst natural disasters in the United States (Galveston, 1900: 8,000 killed; San Francisco, 1906: 3,000 killed; New Orleans, 2005: 1,800 killed).

We don’t expect such losses in a future San Francisco quake because we’ve changed many things since 1872. The main reason Lone Pine experienced such devastation is that so many of its buildings were constructed from adobe bricks. Adobe bricks are basically blocks of dried mud, sometimes mixed with straw. Lone Pine’s buildings could not be made from timber because structural wood was scarce in the region, but mud is always plentiful. However, brick buildings are inherently unstable and dangerous because little holds these blocks in place when an earthquake shifts them, sending heavy walls tumbling down on the delicate bodies of those living in such precarious houses. Making a house out of small, shiftable pieces of masonry is a very bad idea in earthquake country.

Put another way: earthquakes don’t kill people, buildings do.

A second reason Lone Pine suffered so greatly was its proximity to the fault that generated the quake. Today, just a short distance west of the town, one can still see dramatic fault offsets from 1872; a century and a half of erosion has done little to erase the scars created by this giant quake (see Figure \(\PageIndex{1}\)). Lone Pine was simply too close to the fault and absorbed the full energy of the quake.

What happened in the 1872 Lone Pine quake has a lot to teach us about California’s earthquake hazards.

First, like our 1872 predecessors, far too many modern Californians live in seismically vulnerable buildings. Though we no longer build with weak adobe bricks, many California buildings are unreinforced masonry which can collapse in even moderate quakes. And while many residents assume that “the government” will somehow protect Californians from quake hazards through building codes, in some cases the opposite is true. “Soft first story” buildings have foundation levels relatively open and unreinforced. One reason modern buildings are constructed with a soft first story is to accommodate parking underneath buildings. Many municipalities actually require new multi-family buildings to have such parking, meaning that by code California buildings are designed more vulnerable to earthquakes than they need to be.

Second, like the Lone Pine residents unwittingly living right next to a major fault, the majority of Californians live in just a few urban regions that are the among most seismically dangerous regions in the entire state. There are more seismically stable areas of California, but in those regions fewer people reside. We live in the wrong places in the wrong types of houses.

We could have done better. We could have chosen to build this state in a more rational way. We could have learned lessons from California’s rich inventory of historic earthquakes–not just 1872, but also 1700, 1906, 1933, 1971, 1989, 1994, and many more. The history of these quakes could have influenced decisions about development occurred, both in terms of location and also in terms of types of buildings. But California chose instead to grow with little regard to seismic hazard.

Thumbnail: "Hazard map" by USGS is in the public domain.