Geology 9 Exam 2

identify right-lateral strike-slip, left-lateral strike-slip, reverse and normal faults when you are provided with a block diagram or an aerial image of relative offset.

- A left-lateral strike-slip fault is one on which the displacement of the far block is to the left when viewed from either side. - A right-lateral strike-slip fault is one on which the displacement of the far block is to the right when viewed from either side. - normal fault - a dip-slip fault in which the block above the fault has moved downward relative to the block below. - reverse (thrust) fault - a dip-slip fault in which the upper block, above the fault plane, moves up and over the lower block.

explain where an earthquake starts

- Because earthquakes are a phenomenon of brittle, elastic upper lithosphere, they are restricted to the shallow crust. - However, the depth extent of faulting depends on the tectonic setting: - at transform plate boundaries: 0-15 km - at subduction zones: 0-50 km (because of cold oceanic slab) - in extensional regimes: 0-20 km - Note that earthquakes begin at a point, usually at the deeper part of these ranges.

In which of Earth's layers does each type of behavior dominate? How are those layers involved in earthquakes?

- Elastic deformation is the dominant form of deformation at shallow depths in the crust and lithosphere because both the temperature and pressure are low. (rigid upper level lithosphere) -Ductile deformation is in the lower level, asthenosphere - Movement in the mantle caused by variations in heat from the core, cause the plates to shift, which can cause earthquakes and volcanic eruptions.

difference between foreshocks, the mainshock and aftershocks.

- Foreshocks = Smaller earthquakes preceding mainshock Identified in hindsight, after larger main shock occurs Some earthquakes have no foreshocks - Mainshock = Largest earthquake in the sequence - Aftershocks = Smaller earthquakes after a mainshock Can be (more) damaging Are additional adjustments to prior strain or to the new stress state Die out with time after the mainshock

compare and contrast p-waves and s-waves by drawing the motion of a slice of ground as a p-wave passes and as an s-wave passes and listing which types of material p-waves and s-waves are able to travel through.

- P waves can travel through liquid and solids and gases - S waves only travel through solids

how does an earthquake starts, continues and stops. Can you describe the basic forms of energy present before an earthquake versus during an earthquake?

- Plates move in their own separate directions - This differential motion causes high strain at plate boundaries, where plates are in contact - Suddenly, stress > frictional strength and the fault breaks! Much of the rock rebounds to its original position, unstressed position. This is due to rock's elastic behavior (like a rubber band returns to its original shape after pull). - The stored strain energy is released as kinetic energy (energy of motion) in the form of seismic waves. - stops :The rupture continues until enough energy has been released to relieve much of the accumulated strain in the rocks.

What are the 4 actions you should take to be prepared for an earthquake (or any disaster)? Have there been any damaging earthquakes in California over the last century?

- Prepared med-kit - Food- water supplies - Find drop, cover, hold spots in house or building - Know exit strategies San Francisco earthquake of 1906, major earthquake with a magnitude of 7.9 that occurred on April 18, 1906, at 5:12 am off the northern California coast.

what stress and strain are and how they are related to one another?

- Stress is the force applied to a material, divided by the material's cross-sectional area. - Strain is the deformation or displacement of material that results from an applied stress - Strain is related to stress through a constitutive law, which describes how a material behaves. For example, elastic rock and ductile rock have different constitutive laws. The constitutive law for elastic materials is Hooke's Law.

Describe the difference between the Modified Mercalli Scale and the moment magnitude scale for earthquakes. What does each scale measure exactly?

- The Mercalli Scale is based on observable earthquake damage. estimates the shaking intensity from an earthquake at a specific location - The magnitude scale is based on seismic records - Thus, the magnitude scale is considered scientifically more objective and therefore more accurate.

what is offset and how it is helpful in earthquake research.

- The horizontal displacement between points on either side of a fault, which can range from millimeters to kilometers. - they can help undershoot gaps in a survey, or image beneath salt canopies and other recumbent features.

identify the epicenter and the hypocenter (focus) of an earthquake.

- The location BELOW the earth's surface where the earthquake starts is called the hypocenter. - The location directly ABOVE it on the surface of the earth is called the epicenter

What are the two main parts of an earthquake?

- Waves: The waves that you feel during an earthquake. - Fault: A fracture in the rocks that make up the Earth's crust.

write 2-3 sentence descriptions of the 2 ways that we discussed for assessing seismic hazard. What does each one try to estimate? Think of 1 way an engineer or emergency preparedness manager might use each one.

- better/ stronger building design (use triangles)

explain the difference between elastic behavior and ductile behavior.

- elastic: region where the material will return to its original shape when the stress is removed, but can be stretched, bent, or compressed - ductile: the bending and flowing of a material (without cracking and breaking) subjected to stress. deformation that doesn't spring back, but also doesn't break/crack. (Like clay - if you compress it and them release it, it will not return to its original shape.)

list and describe 4 ways that larger magnitude earthquakes differ from smaller earthquakes.

- have long rupture lengths. - cause larger amplitude waves and more long period waves, both increasing the potential for damage. - produce higher ground accelerations. - have higher shaking intensities (on the modified Mercalli scale) - have longer shaking durations (shake the ground for longer). - have more aftershocks. - are much less common than smaller earthquakes - phew!

plastic deformation, and give an example of plastic deformation in brittle rocks and plastic deformation in ductile rocks.

- permanent deformation caused by strain when stress exceeds a certain value - Rolling steel into a particular shape

list the three factors that control the characteristics of the seismic waves recorded on a seismometer as well as the shaking we feel at the same location.

1. Source Energy released during the rupture how energy leaves that fault (angle) 2. Path Distance from the focus Geology between the hypocenter and the site: hard rock or soft sediment 3. Site: Local soil conditions: Sediment: firm, loose, wet, dry, sand, clay, etc Rock: soft rock, hard rock, fractured, etc

What does a seismograph measure?

A recording device that records ALL shaking due to seismic waves.

Why do aftershocks occur? Can you describe 2 properties of aftershock sequences? In other words, what are 2 characteristics of all sets of aftershocks?

Aftershocks occur near the fault zone where the mainshock rupture occurred and are part of the "readjustment process" after the main slip on the fault. Aftershocks become less frequent with time Additional release of energy after mainshock

body waves

Body Waves (travel through Earth) P-waves Primary waves, fastest, travel through solids and liquids, transfer energy by compression (1st to arrive) S-waves Secondary waves, second fastest, only travel through solids, transfer energy in a transverse motion (2nd to arrive)

identify 4 causes of earthquakes

Earthquakes are caused by strain & stress in the Earth, which can be caused by: - Tectonic plate motions - Volcanic activity, including magma migration - Explosions, including bombs - Injection or withdrawal of fluids from the ground

Define attenuation

Reduction of power or intensity as waves travel further from epicenter

explain the difference between seismic hazard and risk.

Seismic hazard is a natural phenomenon such as ground shaking, fault rupture, or soil liquefaction that is generated by an earthquake, whereas seismic risk is the probability that humans will incur loss or damage to their built environment if they are exposed to a seismic hazard

how are strike-slip fault and a dip-slip fault different

Strike slip faults are when rocks move along side one another, while dip-slip is when the rock moves along the dip of the fault.

define surface wave and name at least one type.

Surface Waves (travel only at Earth's surface) Love waves 3rd fastest, only travel through solids ("snake-like" motion) Rayleigh waves Slowest seismic waves, but longest period and travel farthest, very destructive, transfer energy in a backward rolling elliptical fashion, travel through solids and liquids (rolling motion)

Determining factors: of Elastic or Ductile

Temperature: T brittle < T ductile Pressure: P brittle < P ductile Rate of Deformation: Δ brittle > Δ ductile Composition: chemical composition and bonding

Earthquake

The shaking at the surface of Earth, that results from the movement of rock beneath Earth's surface. A slip on a fault that causes vobrations in the ground

state the probability of a M 6.7 or larger earthquake here in the Bay Area over the next 20-30 years.

around 62%

draw a seismogram showing the different first arrival times and relative magnitudes of p-waves, s-waves and surface waves. Which waves are fastest? Which are slowest?

p-waves arrive faster s-waves are slower

What is the difference between these 3 seismometers? How does each type of wave (p-waves, s-waves, surface waves) show up differently on each type of seismometer?

typically records 3 seismometers Records: Up-Dow East-West North-South motion(s). Shows: - Arrivals of different wave types. - Amplitude of waves (magnitude of ground displacement). - Timing of wave arrivals (when the waves first arrive). - Time elapsed between 1st P-wave arrival and 1st S-wave arrival, called the S-P time.

seismic waves

vibrations that travel through Earth carrying the energy released during an earthquake

Draw a simple, periodic (repeating) wave and label a wave's wavelength, period, and frequency on a graph. Recall that you will need two graphs, with different x-axis values, in order to draw both wavelength and period.

x- axis: time/ distance y-axis; displacement