Chapter 12: Earthquakes & Earth's Interior

These will indicate the presence of a fault scarp:

- A "step" in the landscape - Break in slope along a hillside - Freshly exposed, generally linear feature with little/no vegitation

Potential sources of destruction that may be caused either directly or secondarily by earthquakes:

- Aftershocks - Fires - Tsunamis - Landslides & rockfalls

Tsunamis may be generated by:

- Earthquakes that cause the seafloor to shift. - Landslides that displace large amounts of water. - Activity associated with volcano eruptions.

Volcanoes & magma generate earthquakes in what ways?

- Explosive eruptions - Landslides on unstable slopes - Movement of magma within the volcano

If the 3 seismic stations have the following P-s intervals: DUG= 57 sec., WUAZ= 73 sec., ISCO= 4 sec. Place the stations in order from closest station to the earthquake, to the one farthest away:

- ISCO - DUG - WUAZ

Long-range earthquakes forecasting:

- Is based mainly on the knowledge of when & where earthquakes occurred in the past. - Measures patterns of seismic activity along a fault to determine locations & recurrence intervals. - uses tectonic settings & historical records.

What features may be common along active faults, like the San Andreas?

- Linear ridge or valley - Scarp - Offset stream channel - Drainage channels running parallel to fault

Events that would lead to the formation of a tsunami due to an earthquake in order from first to last:

- Megathrust is locked, causing the seafloor to bulge under stress. - Megathrust ruptures, & bulging plate changes shape. - Water above the plate lifts up toward the surface, forming a ridge of higher water. - A tsunami radiates away from the disturbance; not noticeable in the open ocean. - Tsunami approaches the shore; energy concentrates in shallows to create a higher wave.

Rank seismic waves in order of recording by a seismometer:

- P-Wave - S-Wave - Surface Wave

Secondary Earthquake Damage

- Rupture of natural gas lines cause explosions & fires. - Flooding occurs due to failure of dams. - Flooding of dry land occurs as seawater inundates subsided areas.

Direct Earthquake Damage

- Shaking collapses poorly constructed or rigid structures. - Fault scarps or ruptures destroy buildings & roads. - Liquefaction of the ground causes building collapse.

Why does the U.S. have such varying risks of seismic activity?

- Some areas are near plate boundaries, while others are not. - Volcanic activity can cause seismic risk in some areas. - Some regions in the continental interior have active fault systems.

What features in this image help you identify the location of the fault?

- Stream channel running parallel with the fault. - Linear ridges & valley scarp.

Based on this image of an earthquake cycle model, what is true?

- The vertical distance from A to B represents the amount of stress required to overcome the strength of the fault. - The horizontal distance from C to D represents the time between 2 earthquakes. (recurrence level)

Steps taken to measure the local magnitude (MI) of a shallow earthquake (in order):

1. Seismic data are gathered from several seismometers. 2. Maximum amplitude of the S-Wave is measured on each seismogram. 3. Relationships between distance & S-Wave amplitude are plotted on nomograph. 4. MI is the point where each line crosses the center column (magnitude) of the nomograph.

The process of locating an earthquakes epicenter (in order):

1. Select record from at least 3 seismic station. 2. Determine the P-S interval for each station. 3. Estimate station distances from the epicenter using P-S intervals on a time-travel curve. 4. Draw circles around each station, with a radius equal to distance from the epicenter. 5. Locate the intersection of all of the circles to determine the epicenter of the earthquake.

Primary Waves

Body wave; compressional waves; fastest waves.

Secondary Waves

Body wave; movement is perpendicular to direction of travel.

Landslides generate earthquakes by ______________.

Causing the ground to shake.

Most earthquake deaths are caused by ________________.

Collapse of structures.

The sudden release of energy stored in rocks:

Earthquake

Hydraulic fracturing, filling reservoirs behind dams, & injecting wastewater underground are all ways in which humans create ___________.

Earthquakes

When rocks return to their original shapes after being strained, it is called _______ behavior.

Elastic

Strike-Slip Faults

Ex.) 2 sides of the fault move horizontally past one another; fault plane is near vertical; most common along transform plate boundaries.

Thrust Faults

Ex.) Gently dipping faults in which the hanging wall moves up with respect to the footwall; most common along convergent plate boundaries.

Normal Faults

Ex.) The hanging wall moves down with respect to the footwall; most common along divergent boundaries.

Reverse Faults

Ex.) The hanging wall moves up with respect to the footwall; most common along convergent plate boundaries.

True or False: When an earthquake occurs along a fault, the entire plane of the fault slips at once.

False- An earthquake rupture starts in a small area (hypocenter) & expands along the fault over time.

One of the most destructive hazards following an earthquake are _____, which are caused when both natural gas lines & then water mains breaks due to shaking.

Fires

Seismic station

Location of scientific instruments that measure earthquakes.

Hypocenter

Location where an earthquake is generated.

Representing the huge thrust fault created by subduction, __________ earthquakes are deadly & damaging, & commonly creates tsunamis.

Megathrust

Seismic wave

Mode of earthquake energy transmission through Earth.

Epicenter

Point on Earth's surface directly above where an earthquake is generated.

The average time between earthquakes along a certain fault is known as the ___________________.

Recurrence interval

Which fault, located in CA, is both the world's best known & extensively studied? This fault is found along a transform plate boundary & will likely produce a significant earthquake in the next 30 years.

San Andreas

Seismic waves are recorded by a digital instrument called a ___________ & may be viewed either on a computer screen or as a paper plot printout called a __________.

Seismometer; seismogram

The 9.0 magnitude earthquake that occurred northeast of Japan in March 2011 was the result of movement between 2 plates at a ______________.

Subduction zone

Horizontal Waves

Surface waves; material moves side to side.

Vertical Waves

Surface waves; similar to ocean waves as material moves in an elliptical path.

A large sea wave produced by uplift, subsidence, or some other disturbance of the seafloor, especially by a shallow submarine earthquake, is a(n) _______.

Tsunami

Explosive eruptions, landslides, magna movement, & faulting are the causes of earthquakes associated with _________.

Volcanoes

The 2010 & 2011 earthquakes in New Zealand caused a lot of damage because they __________________.

Were very shallow & located near city centers.

Water-saturated sediment can lose its strength due to shaking during an earthquake in a process called ____________.

liquefaction

The 2 basic types of seismic waves include _______ waves, which are created when seismic wave energy reaches Earth's surface & is transformed into new horizontal & vertical waves, & ____ waves, which are usually generated at faults & travel through Earth (primary & secondary).

surface; body