The largest recorded earthquake in the United States was
a magnitude 9.2 that struck Prince William Sound, Alaska on Good Friday,
March 28, 1964 UTC.
The largest recorded earthquake in the world was a
magnitude 9.5 (Mw) in Chile on May 22, 1960.
The earliest reported earthquake in California was felt
in 1769 by the exploring expedition of Gaspar de Portola while the group
was camping about 48 kilometers (30 miles) southeast of Los Angeles.
Before electronics allowed recordings of large earthquakes, scientists
built large spring-pendulum seismometers in an attempt to
record the long-period motion produced by such quakes. The largest one
weighed about 15 tons. There is a medium-sized one three stories high in
Mexico City that is still in operation.
The fastest wave, and therefore the first to arrive at a given
location, is called the P wave. The P wave, or compressional wave,
alternately compresses and expands material in the same direction it is
The average rate of motion across the San Andreas Fault Zone
during the past 3 million years is 56 mm/yr (2 in/yr). This is
about the same rate at which your fingernails grow. Assuming this rate
continues, scientists project that Los Angeles and San Francisco will be
adjacent to one another in approximately 15 million years.
The East African Rift System is a 50-60 km (31-37 miles)
wide zone of active volcanics and faulting that extends north-south in
eastern Africa for more than 3000 km (1864 miles) from Ethiopia in the
north to Zambezi in the south. It is a rare example of an active
continental rift zone, where a continental plate is attempting to split
into two plates which are moving away from one another.
The first “pendulum seismoscope” to measure
the shaking of the ground during an earthquake was developed in 1751, and
it wasn’t until 1855 that faults were recognized as the source of
Moonquakes (“earthquakes” on the moon) do
occur, but they happen less frequently and have smaller magnitudes than
earthquakes on the Earth. It appears they are related to the tidal
stresses associated with the varying distance between the Earth and Moon.
They also occur at great depth, about halfway between the surface and the
center of the moon.
Although both are sea waves, a tsunami and a tidal wave
are two different unrelated phenomenona. A tidal wave is a shallow water
wave caused by the gravitational interactions between the Sun, Moon, and
Earth. A tsunami is a sea wave caused by an underwater earthquake or
landslide (usually triggered by an earthquake) displacing the ocean water.
The hypocenter of an earthquake is the location beneath
the earth’s surface where the rupture of the fault begins. The
epicenter of an earthquake is the location directly above
the hypocenter on the surface of the earth.
The “Ring of Fire” also called the Circum-Pacific belt,
is the zone of earthquakes surrounding the Pacific Ocean — about
90% of the world’s earthquakes occur there. The next most
seismic region (5-6% of earthquakes) is the Alpide belt (extends
from Mediterranean region, eastward through Turkey, Iran, and northern
It is estimated that there are 500,000 detectable earthquakes
in the world each year. 100,000 of those can be felt, and 100 of
them cause damage.
It is thought that more damage was done by the resulting fire after the
1906 San Francisco earthquake than by the earthquake
A seiche (pronounced SAYSH) is what happens in the
swimming pools of Californians during and after an earthquake. It is
“an internal wave oscillating in a body of water” or, in other
words, it is the sloshing of the water in your swimming pool, or any body
of water, caused by the ground shaking in an earthquake. It may continue
for a few moments or hours, long after the generating force is gone. A
seiche can also be caused by wind or tides.
Each year the southern California area has about 10,000
earthquakes. Most of them are so small that they are not felt.
Only several hundred are greater than magnitude 3.0, and only about 15-20
are greater than magnitude 4.0. If there is a large earthquake, however,
the aftershock sequence will produce many more earthquakes of all
magnitudes for many months.
The magnitude of an earthquake is a measured value of the
earthquake size. The magnitude is the same no matter where you are, or how
strong or weak the shaking was in various locations. The
intensity of an earthquake is a measure of the shaking
created by the earthquake, and this value does vary with location.
The Wasatch Range, with its outstanding ski areas, runs
North-South through Utah, and like all mountain ranges it was produced by
a series of earthquakes. The 386 km (240-mile)-long Wasatch Fault is made
up of several segments, each capable of producing up to a M7.5 earthquake.
During the past 6,000 years, there has been a M6.5+ about once every 350
years, and it has been about 350 years since the last powerful earthquake,
which was on the Nephi segment.
The world’s greatest land mountain range is the
Himalaya-Karakoram. It countains 96 of the world’s 109 peaks of over
7,317m (24,000 ft). The longest range is the Andes of South America which
is 7,564km (4700 mi) in length. Both were created bythe movement of
The greatest mountain range in the world, though, is the , extending 64,374 km (40,000 mi) from the Arctic Ocean to the Atlantic Ocean, around Africa, Asia, and Australia, and under the Pacific Ocean to the west coast of North America. It has a greatest height of 4207m (13,800 ft) above the base ocean depth.
As far as we know, there is no such thing as "earthquake weather".
Statistically, there is an equal distribution of earthquakes in cold weather,
hot weather, rainy weather, etc. If weather does affect earthquake occurrence,
we do not yet understand how it works.
From 1975-1995 there were only four states that did not have any
earthquakes. They were: Florida, Iowa, North Dakota, and
The core of the earth was the first internal structural
element to be identified. In 1906 R.D. Oldham discovered it from his
studies of earthquake records. The inner core is solid, and the outer core
is liquid and so does not transmit the shear wave energy released during
The swimming pool at the University of Arizona in Tucson lost water from
sloshing (seiche) caused by the 1985 M8.1 Michoacan, Mexico
earthquake 2000 km (1240 miles) away.
Earthquakes occur in the central portion of the United States too! Some
very powerful earthquakes occurred along the New Madrid fault in the
Mississippi Valley in 1811-1812. Because of the crustal
structure in the Central US which efficiently propagates seismic energy,
shaking from earthquakes in this part of the country are felt at a much
greater distance from the epicenters than similar size quakes in the
Most earthquakes occur at depths of less than 80 km
(50 miles) from the Earth’s surface.
The San Andreas fault is NOT a single, continuous fault,
but rather is actually a fault zone made up of many segments. Movement may
occur along any of the many fault segments along the zone at any time. The
San Andreas fault system is more that 1300 km (800 miles) long, and in
some spots is as much as 16 km (10 miles) deep.
The origin of the name of the San Andreas Fault is often cited as the
San Andreas Lake. However, based on some 1895 and 1908 reports by
geologist A.C. Lawson, who named the fault, the name was actually taken
from the San Andreas Valley. He likely did not realize at the time that
the fault ran almost the entire length of California!
The world’s deadliest recorded earthquake occurred
in 1556 in central China. It struck a region where most people lived in
caves carved from soft rock. These dwellings collapsed during the
earthquake, killing an estimated 830,000 people. In 1976 another deadly
earthquake struck in Tangshan, China, where more than 250,000 people were
Florida and North Dakota have the smallest number of
earthquakes in the United States.
The deepest earthquakes typically occur at plate
boundaries where the Earth”s crust is being subducted into the
Earth’s mantle. These occur as deep as 750 km (400 miles) below the
Alaska is the most earthquake-prone state and one of the
most seismically active regions in the world. Alaska experiences a
magnitude 7 earthquake almost every year, and a magnitude 8 or greater
earthquake on average every 14 years.
The majority of the earthquakes and volcanic eruptions
occur along plate boundaries such as the boundary between the Pacific
Plate and the North American plate. One of the most active plate
boundaries where earthquakes and eruptions are frequent, for example, is
around the massive Pacific Plate commonly referred to as the Pacific Ring
The earliest recorded evidence of an earthquake has been
traced back to 1831 BC in the Shandong province of China, but there is a
fairly complete record starting in 780 BC during the Zhou Dynasty in
It was recognized as early as 350 BC by the Greek scientist Aristotle that
soft ground shakes more than hard rock in an earthquake.
The cause of earthquakes was stated correctly in 1760 by
British engineer John Michell, one of the first fathers of seismology, in
a memoir where he wrote that earthquakes and the waves of energy that they
make are caused by “shifting masses of rock miles below the
Subduction is the process of the oceanic lithosphere colliding with and descending beneath the continental lithosphere.
In 1663 the European settlers experienced their first earthquake
Human beings can detect sounds in the frequency range 20-20,000 Hertz. If
a P wave refracts out of the rock surface into the air, and it has a
frequency in the audible range, it will be heard as a rumble. Most
earthquake waves have a frequency of less than 20 Hz, so the
waves themselves are usually not heard. Most of the rumbling noise heard
during an earthquake is the building and its contents moving.
When the Chilean earthquake occurred in 1960, seismographs
recorded seismic waves that traveled all around the Earth. These
seismic waves shook the entire earth for many days! This phenomenon is
called the free oscillation of the Earth.
The interior of Antarctica has icequakes which, although
they are much smaller, are perhaps more frequent than earthquakes in
Antarctica. The icequakes are similar to earthquakes, but occur within the
ice sheet itself instead of the land underneath the ice. Some of our polar
observers have told us they can hear the icequakes and see them on the
South Pole seismograph station, but they are much too small to be seen on
enough stations to obtain a location.