Exam 3: Earthquake Geology and Seismology

The acceleration due to gravity is 9.8 meters per second squared (32 feet per second squared),which is referred to as 1.0 g and is used as a comparative unit of measure.Earthquake accelerations have never been measured in excess of 1.0 g.

Large earthquakes do not generate body waves energetic enough to be recorded on seismographs all around the world.

P-waves can travel through ________________.

Earthquake-induced ground motions cause buildings to sway at certain periods.In general,the taller the structure,the _______ the period.

The moment magnitude is more accurate than the classical Richter scale because it is tied directly to physical parameters such as fault-rupture area,fault slip,and energy release,and because other earthquake scales use indirect measures such as how much a seismograph needle moves.

The ________ waves advance in a backward-rotating,elliptical motion.

The Richter scale assesses the 1906 San Francisco earthquake and the 1964 Alaska earthquake as both being of magnitude 8.3.However,on the moment magnitude scale,the San Francisco earthquake is probably equivalent to a Richter magnitude 7.8 and the Alaska seism is equivalent to a 9.2.The Alaska earthquake was at least 100 times bigger.

The relation between distance and damage from an earthquake seems obvious: the closer to the hypocenter/epicenter,the greater the damage,but this is not always the case.

In the ________,Steno stated that in an undeformed sequence of sedimentary rock layers,each sedimentary rock layer is younger than the bed beneath it,but older than the bed above it.

Transform faults usually link spreading centers or connect spreading centers with subduction zones.

The biggest shaking event is called "the earthquake," the smaller ones before it are known as foreshocks,and the smaller ones after it are called aftershocks.

Aftershocks are smaller than the main shock in an earthquake sequence.

Faults on which the dominant forces are extensional are recognized by the separation of the pulled-apart rock layers in a zone of omission.These are ____________.

Where the frequencies of seismic waves match the natural vibration frequencies of local geology and buildings,destruction may be great.

The point on the Earth's surface directly above the point where the fault first ruptures is called the ____________.

The duration of the shaking is not a significant factor in damages suffered and lives lost.

The time of day of an earthquake is not a critical factor affecting loss of life from earthquakes.

The velocity of an S-wave depends on the density and resistance to shearing of materials.

Using the S-P timing method,epicenters can be located using seismograms from a minimum of ______ recording stations.

Despite the profound effects that earthquakes have had on civilizations for so many centuries,systematic scientific observations were not made until the early _________ century,when good descriptions were made of earthquake effects on the land.