Chapter 5: Earthquakes
Chapter 5: Earthquakes GEOL 1005
Popular in Environmental Geology
Popular in Geology
This 3 page Class Notes was uploaded by Kerrigan Unter on Monday October 19, 2015. The Class Notes belongs to GEOL 1005 at George Washington University taught by Brown, C in Summer 2015. Since its upload, it has received 30 views. For similar materials see Environmental Geology in Geology at George Washington University.
Reviews for Chapter 5: Earthquakes
Report this Material
What is Karma?
Karma is the currency of StudySoup.
You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!
Date Created: 10/19/15
GEOL 1005 Chapter 5 Earthquakes 51 Earthquake Basics Earthquake trembling shaking or vibration or Earth Seismic waves movements that generate vibrations Focus point underground where the rock first ruptures hypocenter Epicenter point on the Earth s surface directly above the focus Largest earthquakes on record have occurred along subduction zones where one plate slips beneath another and descends into the mantle at a convergent plate boundary Intraplate earthquake originate far from an active tectonic plate boundary Fault trace forms when a fault breaks the surface Elastic rebound theory movement along a fault is the result of an abrupt release of a progressively increasing elastic strain between rock masses on either side of the fault Elastic strain rocks under tectonic stress are increasingly bent and deformed Elastic rebound rocks on either side of the fault unbend as they snap to a new position causing vibrations Earthquake cycle repeated generation of earthquakes by the buildup and release of elastic strain or fault Fault creep the slow and gradual movement along a fault that doesn t cause signi cant earthquakes Body waves travel through Earth s interior P waves primary waves compressional alternatively push and pull rocks along their direction of travel can propagate through a solid liquid S waves vibrate rock perpendicular to the direction of wave movement up and down or side to side Shearing rock deformation Surface waves when body waves approach the Earth s surface travel along Earth s outer edges rather than through its interior Love waves surface waves that vibrate the ground back and forth but not vertically Rayleigh waves propagate across Earth s surface in a rolling motion 52 Investigating Earthquakes Seismometers instruments that measure ground motions cause by passing seismic waves Seismogram record of ground motion measured by a seismometer Strongmotion seismometer used to record ground motions near an earthquake source Motion is measure as acceleration the rate of change of ground motion as the seismic waves vibrate it Period time it takes for one complete peak to peak vibration to pass the seismometer Frequency number of vibrations that the wave completes in one second measure in cycles per second hertz Hz Amplitude height of the peaks re ects the strength of the shaking Magnitude estimated through wave measurements Richter magnitude scale given as whole number with one decimal place logarithmic scale Moment magnitude MW numerical scale of the amount of energy released by an earthquake calculated on the basic of the total area of the fault rupture how far the rocks move along the fault during the earthquake and the strength of the rock that ruptures Intensity degree of shaking effects at a particular location measured in terms of its effect on people and structures Modified Mercalli Scale ranks earthquake intensities on a 12point scale Seismologists can estimate the location of an earthquake s epicenter by analyzing the difference in arrival times of P and S waves The depth of an earthquake s focus is also calculated with data from multiple seismometer stations Seismologist have classified earthquake depths in three categories Shallow occur within the first 70 km of the lithosphere Intermediate 71300 km Deep 301700 km 53 Earthquake hazards The overall size of an earthquake in uences the intensity of ground shaking The deeper the earthquake s focus the less severe the ground shaking Seismic waves change as they pass through different materials Liquefaction can occur when unconsolidated surface materials are poorly drained ans saturated with water Slope failure includes everything from small rock falls to massive muddy debris ows Uplift some areas rise when blocks of the crust shift Subside some areas sink when blocks of the crust shift Tsunami large ocean waves Fires are a major hazard of Earthquakes Severed gas mains and electrical lines are common reasons why fires start 54 Earthquake prediction Precursors variety of possible warning signs The ability to accurately predict the size location and time of earthquakes remain elusive Shortterm prediction specific statement that an earthquake of a given size is imminent within a stated number of hours days or weeks Precursors Increase in the number of small earthquakes on a fault Sharp increase or decrease in the rate of fault creep Fluctuations in groundwater levels Decrease in the resistance of the ground to electrical current Increase in the ground s emission of radon gas or methane Titling or uplifting of the ground surface near a fault Seismic gap any segment of the fault that has not ruptured recently in comparison to neighboring segments Recurrence interval average time between characteristic earthquakes 55 Mitigating Earthquake hazards Base isolation the entire building rests on exible supports that ast as a buffer between the building and the ground Early warning systems Emergency response Public education
Are you sure you want to buy this material for
You're already Subscribed!
Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'