Building for Earthquakes
Collapse of brick structure during 1983 Coalinga
Earthquake
• Chances are 2 out of 3
that you’ll be home
when the next
earthquake strikes, and
1out of 3 that you’ll be
in bed. So your home’s
ability to withstand an
earthquake affects not
only your pocketbook
but also your life and
the lives of those who
live with you.
• Imagine for a moment that
your house is anchored to a
flatcar on a moving train.
Suddenly the train collides
with another train and the
flatcar stops abruptly.
What happens to your
house? If it’s a woodframed house, as most
houses in California are, it
probably would not
collapse, although your
brick chimney might
topple over.
Damage to chimneys resulting from magnitude 7.1, 1992
Petrolia Earthquake
This house along Jefferson Street in the Marina
District shifted more than 10 cm on its foundation
due to 1989 Loma Prieta Earthquake
Wooden structure located on Jefferson Street in
Watsonville has shifted on its foundation due to
1989 Loma Prieta Earthquake
• This analogy introduces an
important concept. The jolt to
your house during the train
wreck is analogous to the
shocks the house would
receive during a large
earthquake. The response of
the house and its contents
(including you) to these jolts
follows the principle of inertia.
The principle of inertia says
that a stationary object will
remain stationary. A home not
bolted to its’ foundation will
slip of the foundation because
of its’ inertia.
Damage to unreinforced masonry structures in
Los Gatos (above) and San Jose (below) resulting
from the 1989 Loma Prieta Earthquake
• Ductile buildings such as
wood and steel-frame
structures tend to bend and
sway during an earthquake.
In contrast, brittle structures
made of brick or concrete
block joined together with
mortar, or adobe buildings
from California’s pioneer days
are unable to deform during
an earthquake with out
collapsing.
The Armenian SSR Earthquake
• On December 7, 1988, at
11:41 a.m. local time a
magnitude 6.9 earthquake
shook northwestern Armenia
and was followed four
minutes later by a magnitude
5.8 aftershock. Swarms of
aftershocks, some as large as
magnitude 5.0, continued for
months in the area around
Spitak. The vast majority of
the damage occurred in
unreinforced masonry
structures.
• In this earthquake both
design deficiencies and
flawed construction practices
were blamed for the large
number of building collapses
and resulting deaths. Many
of the modern multi-storied
buildings did not survive.
Twenty-five thousand were
killed and 15,000 were
injured by the earthquake. In
addition 517,000 people
were made homeless.
Partial collapse of Bullocks Department Store
Collapsed roof near Northridge Mall
• During the 1994
Northridge
Earthquake, similar
damage patterns to
those in Armenia
were observed
throughout the San
Fernando Valley.
• A common failure in
California’s recent
earthquakes was the two- or
three-garage with living
space overhead. Many
condominiums have most of
the first floor devoted to
parking, with apartment
space in the upper floors.
The large amount of empty
space at the garage door
Detail of shoring to garage area in building on
means less bracing against
Beach Street in the Marina District. The practice of
earthquake forces than in
using the first floor for garages left the building with
standard walls, so these
inadequate lateral bracing on the ground level.
open areas are the first to
fail in an earthquake.
Carport beneath the collapsed apartment building in Northridge. Collapse of buildings into carports
was a common cause of apartment damage in the epicentral area. The carports, because they were
open on one side, did not have the resistance to shaking.
This apartment building in Reseda collapsed over the
garage due to 1994 Northridge Earthquake
Porch Damage, Wood Frame House, Santa Cruz
Mountains, Loma Prieta Earthquake, 1989
Total Collapse of Front of Residence, Coalinga
Earthquake of 1983
• Similar problems
arise, although on a
smaller scale, with
large picture windows,
sliding-glass patio
doors, double doors or
patio covers.
Soil Types and Shaking
Amplification
• Because of certain
conditions, seismic waves
may cause certain areas to
shake up to 10x harder
during an earthquake, this
is called site amplification.
The chief contributor to
the site amplification is
the velocity at which the
rock or soil transmits
shear waves (S-waves).
Shaking is stronger
where the shear wave
velocity is lower.
The National Earthquake Hazards Reduction Program (NEHRP) has
defined 5 soil types based on their shear-wave velocity (Vs). We have
modified these definitions slightly, based on studies of earthquake damage
in the Bay Area. The modified definitions are as follows: A) Vs > 1500
m/sec (This soil type occurs infrequently in the bay area. We consider it
with type B. They are both represented by the color blue on the map). Soil
type A includes unweathered intrusive igneous rock. Soil types A and B do
not contribute greatly to shaking amplification.
B) 1500 m/sec > Vs >
750 m/sec. Soil type B includes volcanics, most Mesozoic bedrock, and
some Franciscan bedrock. (Mesozoic rocks are between 245 and 64
million years old. The Franciscan Complex is a Mesozoic unit that is
common in the Bay Area.)
C) 750 m/sec > Vs > 350 m/sec. Soil type C
includes some Quaternary (less than 1.8 million years old) sands,
sandstones and mudstones, some Upper Tertiary (1.8 to 24 million years
old) sandstones, mudstones and limestone, some Lower Tertiary (24 to 64
million years old) mudstones and sandstones, and Franciscan melange and
serpentinite.
D) 350 m/sec > Vs > 200 m/sec. Soil type D includes some
Quaternary muds, sands, gravels, silts and mud. Significant amplification
of shaking by these soils is generally expected.
E) 200 m/sec > Vs. Soil
type E includes water-saturated mud and artificial fill. The strongest
amplification of shaking due is expected for this soil type.
Fire!
Citizens of San Francisco watch fires burn out of
control following the 1906 earthquake
Fires burn in the city of Kobe
following the 1995 quake there
• There is also a
formidable threat of fire,
such as resulted from the
1906 San Francisco, the
1923 Tokyo, and the
1995 Kobe earthquakes.
This panoramic view shows San Francisco in flames, five hours after the earthquake. The photograph was
taken from Mason Street at 10:00 A.M., April 18, 1906. There is little evidence of earthquake damage.
Most of the city's downtown buildings appear to be intact, yet these were later partially or wholly
destroyed by flames. The fire continued unchecked for three days.
This view of the San Francisco ruins shows many square blocks completely leveled. The photograph was
taken on May 1, 1906, almost a month after the disaster. Much of the debris had already been hauled
away leaving only empty ash-blackened blocks. Rebuilding of small buildings had begun.
Great Kanto quake (TokyoYokohama) 1923
killed at least 140,000
tens of thousands burnt to
death
Great Hanshin quake (Kobe)
1995
Kobe
fires started in old, cramped
parts of city
many wooden buildings
146 fires started
23,000 homes destroyed
Tokyo today
~ 1 million wooden homes
Tokyo