Travel 1 0 | Sunday, April 16, 2006
The Orange County Register
Special Report | SAN ANDREAS FAULT TOURING THE MIGHTY
SAN ANDREAS
First hit The first bump is the fastest of the seismic waves, called Primary, or P, waves.
FAULT
Major jolt The next set is usually larger lines, called Shear, or S, waves.
Finishing up Surface waves are the slowest and usually come last. If a quake is close to the surface, these waves can be very large.
A
hundred years ago, the San Francisco quake gave birth to the modern study of earthquakes and led to the discovery of the San Andreas fault. But temblors haven t simply shaped California s landscape, they have affected its culture as well. When an earthquake strikes, many Californians nonchalantly ride it out. After the shaking ends, one sport is to guess the magnitude and epicenter. Here are tips on what you can tell from the rocking and on sights around the Golden State honoring the phenomenon that, every so often, shakes up our lives.
Riding it out
How an earthquake feels depends on factors such as proximity to the fault, surrounding geology and size of the quake. The first thing you might notice is a thunderous clap and rattling windows. This is energy from the P waves pushing through the Earth, transferring into the air, creating a sound wave. The closer to the epicenter, the louder the bang. Next come the S waves packing the most energy and causing the most extreme shaking.
Major quakes and points of interest
Estimate the miles you are from the quake s center by counting the seconds between the P and S waves, then multiply by 5.
California has thousands of faults, but the largest is the 800-mile San Andreas. Here are locations of the 160 quakes magnitude 5.5 or higher that have struck since 1800 near the fault and quake-related sights to check out:
Seismic waves
0
7.1
QUAKE KEY
xx 7.2
7.0 18 99
7.3
1980
A quake s duration is related to the length of fault affected. You can estimate the length of fault involved by multiplying the seconds a quake lasts by 1.5.
MAGNITUDE 5.5 to 6.9
1991
xxxx MAGNITUDE 7.0 TO 7.9 AND DATE
1923
Shelter Cove Northernmost point at which fault touches land.
7.2
7.1
1992
San Andreas fault
Fort Ross
7.8
7.0
San Francisco
7.0
1989
1838
Newport Beach
7.1
San Francisco San Jose Riverside
San Juan Bautista
Coalinga
L.A. moving to S.F.?
North American Plate Paso Robles
Palmdale
The Pacific Plate is creeping northwest past the North American Plate at an average rate of 2 inches per year. In the 1906 San Francisco quake, the plates in some places moved 21 feet. Scientists estimate that it will take about 12 million years before Los Angeles and San Francisco are side by side, geographically at least.
Here are comparisons of three quakes and how much of a fault might be affected: miles of fault 8.0 300 900 times the energy of a 6.0
7.9
7.1
7.1
Santa Barbara 1812
energy of a 6.0
6.0
5 miles of fault
Palmdale: North of Lake Palmdale is a ridge known for its famous road cuts. The fault is visible as a line curving through the rocks.
1857
1927
30 miles of fault
7.0 30 times the
Fort Tejon Camel-riding U.S. Army troops reported 1857 quake.
7.6 18 72
San Luis Obispo
7.2
7.2
1992
7.1
1999
Wrightwood Ski resort is San Andreas highest point
1999
Riverside Los Angeles
Desert Hot Springs Fault runs through center of town Dos Palmas Preserve Warm water bubbles up as a result of the fault Bombay Beach Funky seaside town
Palm Springs
Newport Beach
Patterns to California s big quakes? Courtesy of Bancroft Library
OUT OF CONTROL: Fires rage through San Francisco buildings after the
Predicting earthquakes is still difficult, but there is no doubt that earthquakes happen in clusters. Scientists have been trying to read the patterns to help make predictions.
devastating 7.8-magnitude earthquake on April 18, 1906.
Number of quakes 5.5 or higher 7 6 5 4
1857 Fort Tejon quake: Packing a bit more punch than the famous 1906 quake, it ruptured the San Andreas fault near Parkfield, displacing 29 feet and killing one person.
1872 Owens Valley quake: Thirdstrongest quake in California history destroyed 59 adobe and stone houses. Displaced 23 feet in Lone Pine, killed 27 people.
Sniff around for gas leaks, starting with the water heater. If you smell gas, turn off the valve and call the Gas Co. Open windows and stay outside until house airs out.
Magnitudes of scale
Carrizo Plain: One of the best places to see the fault particularly the streams that were abruptly shifted by the 1857 Fort Tejon quake is from the sky. Wallace Creek is one of the most dramatic offset streams on the fault.
San Juan Bautista
San Diego
Unreinforced masonry such as some chimneys poses a danger because it might collapse. Stay away until structural integrity is confirmed.
A common problem is broken glass everywhere don t investigate in bare feet. Check for spilled toxic liquids, such as bleach, that give off fumes that can incapacitate.
Parkfield: Self-proclaimed earthquake capital of the world. At the bridge that leads into town is a sign that says San Andreas Fault. Now Entering North American Plate. The Parkfield Cafe features dishes named with earthquake lingo, like the Richter Pork Chops.
Fort Ross
Pacific Plate
Be careful of overhead electrical wires that might have loosened they are deadly.
Palo Alto: The fault, seven miles up Page Mill Road outside Palo Alto, is apparent from a 700yard dip in the road. Drive to Los Trancos Open Space Preserve (free trail map at the entrance), a good place to see the fault.
1868
1906
Paso Robles
Los Angeles
Safety tips for after the quake:
Sacramento: An exhibit on the 1906 San Francisco earthquake opens Saturday at the State Capitol Museum. It will mark the centennial of the quake and include photographs, artifacts and accounts from survivors.
Point Arena
Eureka
Post-quake
Point Reyes National Seashore: Visitors can walk a trail along a rupture from the 1906 quake. A fence that was transformed by the quake into a zigzag shape is a must-take photograph.
7.3
1994
Santa Barbara
Energy transferred in sound waves
POINT OF INTEREST
Eureka
1922
100
MILES
7.1 San Diego
12 5.5 or higher quakes in 1954 1906 San Francisco quake: Most devastating quake in U.S. history led to discovery of the San Andreas fault. Fire and quakes killed an estimated 3,000 people.
1952 Kern County quake: Twelve people killed and $60 million in damage when Bear Mountain moved upward, displacing 325 yards of highway.
18 92
MEXICO
1940
7.8
7.0 1934
Mexicali
What s a major quake? Although many remember the 1933 Long Beach, 1989 Loma Prieta and 1994 Northridge quakes as significant, these quakes affected only a short distance of fault, so seismologists don t consider them major quakes. The 1999 Hector Mine quake near Twentynine Palms affected a large distance on the fault line, a major quake for scientists, but its remote location meant it had little impact.
Circles denote at least one quake was 7.0 or higher
3 2 1 0
00 08 12 27 36 38 52 55 56 57 58 60 61 62 64 65 66 68 69 70 71 72 73 75 78 81 82 83 84 85 87 88 89 90 91 92 93 94 96 97 98 99 01 03 06 07 08 09 10 11 14 15 16 18 22 23 25 26 27 32 33 34 35 36 37 40 41 42 45 46 47 48 49 51 52 54 56 59 60 66 68 71 73 76 79 80 81 83 84 85 86 87 89 91 92 93 94 95 96 97 99 00 03 04 2000s 1800s 1900s
Sources: Susan Hough, U.S. Geological Survey, author of Finding Fault in California; ESRI; Michigan Tech; Orange County Red Cross; U.S. Department of the Interior NOTE: Two U.S. Geological Society data tables were used to plot quakes. The summary magnitude from California Earthquakes From 1769 To Present was used to create the chart and to plot earthquake locations on the map. Since some of those magnitudes were measured on a different scale than the Richter scale, updated numbers from Earthquakes in the United States, Magnitude 7.0 and Greater were used to determine quakes with magnitudes 7.0 and higher.
Reporting by Chantal Lamers; graphic by Scott M. Brown / The Register