Chapter 8

A tsunami is a special kind of tidal wave caused by the gravitational attraction of the Sun not the Moon. can get big but never bigger than 30 feet high. is dangerous near its source but dies out within about 200 miles. may be just a broad, gentle swelling out at sea but grows as it approaches shore.

Earthquake prediction is not highly reliable, but geologists do know that earthquakes never happen outside of seismic belts. that recurrence intervals can provide accurate short-term predictions. that swarms always precede major earthquakes and can help with short term prediction. more earthquakes happen along plate boundaries than happen at intraplate locations.

Examining sedimentary bedding in a geologic study reveals disrupted layers formed 260, 820, 1,200, 2,100, and 2,300 years ago. What is the recurrence interval of the earthquakes that caused the disruption? 200 years 380 years 510 years 560 years

Friction is slow but steady movement along a fault. is the force that resists sliding along a surface. is the process by which faults release energy. happens when rock is weak and can slip smoothly, without creating shock waves

Identify the FALSE statement. Normal faults result from stretching the Earth's crust; thrust faults from squeezing and shortening it. Any given earthquake can have more than one magnitude, but can have only one intensity. Moment magnitude (MW) rating is considered the most accurate representation of an earthquake's magnitude. All earthquake magnitude scales are logarithmic, which means a difference of one unit in magnitude reading represents a 10-fold difference in ground motion.

Identify the FALSE statement. Seismic waves become smaller in amplitude with increasing distance from the epicenter. Earthquake magnitude is based on ground motion recorded by a seismograph; intensity is based on the amount of damage produced. Contour lines representing Mercalli values are used to delimit zones of quake intensity; the greater the quake, the higher the intensity values and the wider the zones. Earthquakes never have hypocenters (foci) deeper than about 100 km (60 miles).

Identify the FALSE statement. Long-term earthquake predictions are unreliable and do not provide useful information. are based on the identification of seismic zones. are based on the study of historic recurrence intervals. involve looking for sand volcanoes and disrupted bedding in the area.

Identify the FALSE statement. Seismometers may be the mechanical type, consisting of a weight, spring, frame, pen, and revolving cylinder. may be electronic, consisting of a heavy cylindrical magnet and a coil of wire which produces a signal that can be recorded digitally. are only sensitive enough to record ground movements down to about 1 mm. operate because of inertia; one part of the instrument remains motionless while the recording device moves in response to seismic waves.

Identify the FALSE statement. The Richter scale measures the size of a quake in terms of the damage it does (its intensity). measures the amplitude of the largest deflection on a seismogram in response to specifically defined seismic waves at a specifically defined distance and depth. is today termed a local magnitude reading (ML). works well only for shallow, nearby earthquakes.

Identify the FALSE statement. The tsunami event of December 26, 2004, in Indonesia involved a monstrous magnitude 9.3 earthquake that lasted 9 minutes. was first noticed as a withdrawal of the sea along the beach front. consisted of near-field tsunamis that affected the island of Sumatra and later far-field tsunamis that struck all along the Indian Ocean coast. crippled a nuclear power plant, and released radioactivity into the surrounding environment.

The locations of major earthquakes can be anywhere on the globe. are usually along plate boundaries. are usually toward the centers of tectonic plates. always mark places where plates are converging, never where they're diverging.

Which of the following is NOT a good technique for building earthquake-resistant structures? Use concrete-block rather than wood-frame construction. Bolt bridge spans to the top of support columns. Wrap bridge supports with steel cables. Use supports that are capable of holding more than the static (unmoving) weight of the building.

Which of the following statements is FALSE regarding the 2010 Haiti earthquake? The event was so destructive because of poor construction standards. Faulting occurred along a transform boundary between the Caribbean and North American plates. The earthquake generated a tsunami that was responsible for the majority of the lives lost. The likelihood of an earthquake was great because stress had been building on the fault for over 200 years.

Which of the following statements is TRUE? Earthquakes in California are the result of reverse faulting along the San Andreas fault. the result of widening along the San Andreas fault, which will eventually cause western California to sink into the ocean. always above magnitude 7.5 because the San Andreas is such a large fault. shallow and occur in the upper 15 km of crust, even though the San Andreas fault cuts through the crust to deeper depths.

Which statement concerning tsunami events is FALSE? The velocity of a tsunami wave increases when the wave enters shallower water. Tsunamis may be generated by underwater earthquakes, volcanic explosions, or submarine landslides. Tsunami waves can be 100 to 1000 times wider than typical wind-driven waves, when measured perpendicular to the wave. Tsunamis can travel as fast as jet planes (several hundred miles per hour).

Which statement is FALSE? Liquefaction can cause sediment to turn into an unstable slurry incapable of supporting weight. increases the pressure of the water that fills the pore space between sediment grains. can cause roads, fences, and pipelines to crack and separate if they straddle a fault. can affect sand layers below ground surface and cause them to erupt as sand volcanoes or sand boils

Which statement is TRUE? R- and L-waves are surface seismic waves. S-waves are compressional body waves; P-waves are shear body waves. Surface waves are the first to show up on a seismogram recording of a quake. Shallow-focus quakes do less damage than deep-focus quakes.

Which statement is TRUE? P, S, L, and R are all body waves that pass through the Earth's interior. The hypocenter (focus) is the point on Earth's surface directly above the epicenter. Body waves pass through Earth's interior, whereas surface waves travel at the Earth's surface. S-waves travel twice as fast as P-waves.