Earthquakes & the Hayward Fault

Presented by the UC Berkeley Seismological Laboratory Flour Mill, 1868 Hayward EQ Courtesy of NISEE, EERC, UC Berkeley

What is an earthquake?

• An

earthquake

is what happens when two blocks of the earth suddenly slip past one another. The surface where they slip is called the

fault

or

fault plane

. • The location below the earth’s surface where the earthquake starts is called the

hypocenter

, and the location directly above it on the surface of the earth is called the

epicenter

.

What causes earthquakes to happen?

Answer:

PLATE TECTONICS

!

Plate Tectonics cause strain to build up  Earthquakes relieve strain • The surface of the earth is made up of many different pieces, like a puzzle, that keep slowly moving around, sliding past one another and bumping into each other. These puzzle pieces are called

tectonic plates

.

• Since the edges of the plates are rough, they get stuck while the rest of the plate keeps moving. Finally, when a plate has moved far enough, the edges unstick on one of the faults and there is an earthquake!

The Tectonic Plates

Why does the ground shake during an earthquake?

When the force of the moving tectonic plates finally overcomes the friction of the jagged edges of the fault and it unsticks, all that stored up energy is released. The energy radiates outward from the fault in all directions in the form of

seismic waves

like ripples on a pond. The seismic waves shake the earth as they move through it, and when the waves reach the earth’s surface, they shake the ground and anything on it, like our houses and us!

• Two types of seismic waves that shake the ground in different ways as they travel through it:

P waves

and

S waves

. (see diagram) Example of a large earthquake:

See the YouTube video on our videos page

• P waves are faster than S waves and less destructive during an earthquake because of their considerably smaller amplitudes.

• P waves in the earth’s crust travel 5.5km/s or 12,375mph and S waves travel 3.3km/s or 7,425mph. That means that P waves in the crust travel 24 times the speed of a jumbo jet!

Three Main Types of Faults

A.) Strike-slip Fault : caused by horizontal compression, the two blocks of rock move QuickTime™ and a TIFF (U ncompressed) decompressor are needed to see this picture.

laterally past each other- the San Andreas and Hayward fault are both strike-slip faults B.) Normal Fault : caused by extensional forces pulling the two blocks apart, one block drops down in relation to the other- this type of fault forms mid-oceanic ridges C.) Thrust (Reverse) Fault : caused by compressional forces that shorten the two bodies, pushing one block up relative to the other

How are Earthquakes Measured?

By Intensity INTENSITY

(measures amount of shaking)

- Based on observations of shaking/damage - Location dependent - Designed to relate earthquake intensities to what average person or building experiences.

- A more qualitative scale than the Richter magnitude scale, lacking energy levels associated with various earthquake intensities.

How are Earthquakes Measured?

Using Seismometers • Seismologists use instruments called

seismometers

to measure and record ground movement during an earthquake as a result of seismic waves. They measure very tiny vibrations of the earth and tell us how the ground moves in all directions (up/down, east/west, north/south).

• Seismometers are usually placed in very quiet locations: vaults, underground in tunnels, boreholes, buildings, and the bottom of the ocean.

Seismometers over time • The signals from all of these seismometers are recorded by special computers, and scientists analyze this digital data to determine the size of an earthquake.

How are Earthquakes Measured?

By Magnitude MAGNITUDE

(size of the EQ at its source)

• Seismometers record magnitude • One number describes the quake • Same number regardless of seismometer location • Bigger magnitude means:  bigger affected area  longer rupture time  bigger offset seismogram • A logarithmic scale  amplitude increases by factor of 10 for each magnitude unit  energy increases by factor of 30 for each magnitude unit  for example, a magnitude 6 earthquake releases 30 times the energy of a magnitude 5 and has 10 times greater amplitude

Where do the biggest earthquakes occur?

• About 90% of the world’s earthquakes and 80% of the largest earthquakes, occur on the

“Ring of Fire , ”

an area along the plate boundaries that encircles the basin of the Pacific Ocean.

• The largest events: 1960 Chile (M 9.5), 1964 Alaska (M 9.2), 2004 Sumatra (M 9.1) • China earthquakes (1556 Shensi & 1976 Tangshan) both had close to one million fatalities.

Where are we in all this? Earthquakes in California

• California is very seismically active.

• The majority of large earthquakes in California occur near the coast.

1906 1868 1872 1857

E arthquakes in the San Francisco Bay Area

• The Bay Area is home to many different faults including: San Andreas Fault, Calaveras Fault, and the Hayward Fault. Bay Area EQs in the 75 yrs. before 1906

The impending “Big One”: A Ticking Time Bomb

• The Hayward Fault is a ticking time bomb: stress is continually building up on the Hayward Fault.

• A large earthquake is inevitable, but the question is when will it happen?

Forecast for the “Big One”

• There is a 63% chance that a large earthquake (magnitude 6.7 or greater) will occur between now and 2036 in the Bay Area.

• There is a 31% chance that it will occur on Hayward Fault.

The Hayward Fault

• A major strike-slip fault that runs through the East Bay, including the UC Berkeley campus and football stadium • 3 - 9 mm/year surface creep along Hayward fault  Creep at Memorial Stadium (see picture of displacement of two sections) • Most likely Bay Area fault to produce an earthquake in the future • Last major earthquake on the Hayward Fault was in 1868 (M ~7.0), and it was called the “Great San Francisco Earthquake” until 1906, when the real Great SF Earthquake hit on the San Andreas Fault • Since there have not been any earthquakes > M5 on the Hayward Fault since 1868, that means another “Big One” is coming soon… Image: Google Earth Hayward Fault Tour

Creep on The Hayward Fault

• On Strike-slip Faults (like the Hayward Fault), there is something else in addition to earthquakes that relieves strain from plate tectonics:

Creep

.

• According to the USGS, creep is basically “slow, more or less continuous movement occurring on faults due to ongoing tectonic deformation.”

1974

Creep on the Hayward fault during 30 years.

(about 2.5mm/yr.) Image Courtesy of Doris Sloan Image Courtesy of Doris Sloan But…even though creep relieves strain, it does not relieve enough stress to prevent a large earhquake! So…large earthquakes can still occur on creeping strike-slip faults.

Paleoseismology: A History of Hayward Fault EQs

Scientists can use paleoseismology to determine information about past earthquakes by drilling several meters into the Earth and observing different layers.

Photo Courtesy of Peggy Hellweg Photo Courtesy of Rick McKenzie Hayward Fault History: • 1836 (M?) • 1868 (M~7.0)

Earthquakes Relieve Stress

• Earthquake relieve stress on faults, but small earthquakes cannot relieve enough stress to prevent a large one (big earthquake is inevitable) • For example, you would need about 32,000 magnitude 4.2 earthquakes to equal the energy released by one magnitude 7.2! • Over 10 years, that would mean about 9 earthquakes with magnitude 4.2 a day!

• A magnitude 7.0 earthquake slips about 90cm, but a magnitude 4.0 earthquake slips only a few millimeters.

Graph shows stress levels greatly decreasing after each major earthquake

Hayward Fault Earthquake Simulation Geology + Math + Physics + Supercomputers (which create 3D models of the fault) = Fault Rupture Simulations

See the video on our videos page

Image Courtesy of USGS

Hayward Scenario: Residential Damage

There will be more damage in the East Bay than in San Francisco, since the East Bay is closer to the fault.

Residential damage occurs over a smaller area than for commercial buildings.

Why? Residential building are generally wood framed = less damage Image Courtesy of USGS

Another Issue: Chaos on the Freeways

6 million vehicles in the Bay Area = about 1 million people on the roads  pile-ups everywhere Photo: USGS Also, many bridges and overpasses collapse!

Photo: USGS Photo: USGS

Which Bay Area freeways would be affected?

I-80 through Berkeley Approach to Bay Bridge 101 south of San Fran Approaches to San Mateo Bridge

What will happen to Bay Area bridges?

Bay Bridge The new eastern section of the Bay Bridge, which is expected to open in 2013, is being built to withstand a major earthquake. The retrofit of the western segment has been completed. The Bay Bridge is considered an emergency "lifeline" route to be used in disaster response activities. Thus, when completed, it will be able to reopen quickly following an earthquake. Photo: USGS Bay Bridge in Loma Prieta EQ 1989 For more information, visit: http://baybridgeinfo.org/faqs

Problems to be ready for when the EQ hits:

•Our homes and buildings are much stronger and better designed than those in the past; however, as the Kobe video showed, large ground motion can send furniture and smaller objects flying. So, you should be sure to secure large furniture to walls and carefully store breakable objects.

•Many injuries from earthquakes during the night come from cut feet. Keep a pair of old shoes under your bed just in case!

•It is likely that emergency help may not be available for over 72 hours following a damaging earthquake, so you should have enough water and food stored in an earthquake kit.

•Basic utilities such as electricity, gas, and water can take weeks to recover, so be prepared.

How can you prepare yourself for an earthquake?

Image Courtesy of USGS “The best protection against the danger of earthquakes is not the knowledge of the particular dates upon which they will occur, but the realization that they may occur at any time.” Andrew Lawson, 1922 ABAG Red Cross