Information on Hayward Fault
by Heidi Stenner, Consultant
Check out the USGS
site where you can zoom in along the entire Hayward fault map
1. Where is the fault and what exactly is a fault?
2. How do we know that the fault is there?
- In the big picture, scientists know where the
fault is because of curbs and streets being offset from fault creep,
pre-development aerial photos showing creeks shifted and other
markers of fault movement, and from previous trench exposures
showing the fault below ground (like at the exhibit).
- In the exhibit's trench, we know where the
fault is due to the contrast of sediments across a sharp line.
the west of the fault the sediment is dark in color, gravelly and
sandy, and has visible layers (these are the 9000 year-old creek bed
for ancient Alameda Creek. To the east of the fault the sediment is
tan, and has little gravel or visible layers (these are flood
sediments from Alameda Creek 4000 years ago). They are different
because due to fault movement, two parts of the earth from different
areas have been brought next to each other.
3. What happened in the last big earthquake on the
- The last big earthquake along the Hayward
Fault was in 1868. It was approximately a magnitude 6.9.
- The fault broke for about 30 miles from
around Milpitas to the Oakland-Berkeley border. The fault slipped 3
to 6 feet along the fault. The western side moved north and the
eastern side moved south.
- At the exhibit, the fault slid about 3 feet.
It was closer to San Leandro where the fault slipped about 6 feet.
This is what is likely to happen in the next big quake along the
4. What is a fault creep?
- Fault creep is the slow, almost constant
movement along a fault without large earthquakes. Creep is unusual.
- Most faults around the world only slip during
earthquakes generally larger than magnitude 6.7. The Hayward Fault
slips both during those large earthquakes and also the rest of the
time from fault creep.
- The Hayward Fault in Fremont creeps about
3/16ths of an inch (5mm) per year. The fault needs to move about
6/16ths of an inch (9mm) per year to release the energy building up
at the surface.
- Fault creep is only happening in the upper
couple of miles of the fault's total 8
depth, at least for most of the length of the fault. The lower part
of the fault is locked and has to release energy during bigger
- You can see results of fault creep near the
exhibit. Both the edges of the parking lot island (next to the
exhibit) and Sailway Drive (between Paseo Padre Parkway and the
parking lot) are offset due to fault creep.
5. When is the next big earthquake?
- Wouldn't we all love to know! Unfortunately,
we cannot predict earthquakes.
- Scientific studies have shown that over the
last 2000 years, the Hayward fault has been causing large
earthquakes (magnitude 6.7 or larger) every 125-175 years, on
average. The last big earthquake, in 1868, was 138 years ago
- Bottom line: we are in the time window when
the next one can happen. This is why we need to be prepared!
6. What should I do to be prepared?
- Keep emergency kits (water, radio,
flashlight, etc.) at home, work/school, your car - anywhere you
could likely be caught during an earthquake.
- Develop a family plan. Identify the person
everyone should call to stay updated (out-of-state number if
possible). Identify where everyone should try to meet after the
earthquake and how they could get there.
- Prepare your house and office to reduce the
likelihood of large objects hitting you where you frequently sit or
sleep when strong shaking begins. Determine if your house needs
strengthening to withstand heavy shaking.
Links for more detailed information on being prepared:
Prepare Bay Area
- lots of detailed information on preparing (Red Cross)
Be Prepared for 72 Hours - easy to use
information on preparing
Putting Down Roots in Earthquake
Country - all around wonderful resource/reference for living with
earthquakes (U.S. Geological Survey)
Understand What Could Happen at Your Home
- shows different hazards for your address/area (Association of Bay Area
Understand for What You are
Videos of What
it Could Be Like at Your Home - shaking in a large earthquake is strong!
Prepare The Inside of Your Home
Retrofit/Improve Your Home's Safety (includes retrofitting plans)