seismology

elastic reboudn theory

relative motion across a fault locked by friction actumulates elastic stress in the form of deformation. when the stress exceed the friction the fault slips and reases the energy as a sepctra of siesmic waves

what is the wave trend with increaign magnitudfe of EQs

greater energy in longer wavelength waves

Ritcher magnitude

first magnitude scale built for california. used for a wood anderson seismograph at 100 km form the epicenter

EQ Magnitude scale

attempts to quantify the energy released by and EQ Objective measure

limits of wood anderson

its sensitive to high frequency p waves(high absorbtion and spreading) so its not good for long distances or small EQs

suface wave magnitude

good for long distances and long wave length rayleih waves at distances greater than 2000 km form the epicenter

problem of surface wave mag

not good for deep eqs bc Raylieh waves are poorlh generated

what role do the contastants play in the formulas

various factors calibrate the scales so they are approximately the same when they apply

what problem arrises from EQ scales that are based on fixed periods

for large EQ the scales can saturate meaning they do not “see” what thier max calibration is

moment magnitude

relates to the fundimental properties of the source and therefore does not have saturate

how is moment magnitude determined

from studyign the source/ or with spectral analysis of long period waves

Gutenberge ritcher relation

the frequecy of en EQ above a given magnitude deacreases logrythmicly with magnitude

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used to predicit the occarance of Large EQ when no have been observed usighn the occarfence of smaller EQS

magnitude energy relationship

energy increases exponentially with magnitude many small EQ will not substanitally reduce the hazard of a large EQ

MMI

intensity based onbserved affects, subjective measure at a location

Intestiy increases with what factors

proximity to the EQ, Magnitude of the EQ, loose soils compared to bedrock

Hyposcenter vs epicenter

hypo is a 3d location while the epicmnter is the location on the surface of the earth

how to locate local EQ

within 100km where vp and vs are known and approximatly constant so with can use the arrival tiem difference adn velocities to find the distance. we use Equation of circles with the distance as the radius to find the epicneter. we can also do this graphicly

Distannt EQs

Velocity are no longer constant and therefore we need to use time distance curves that are calculated by refference velocity modles to find the the Distance using the s p tiem diffrence. velocity

PcS and SKP

SKiKS SKIKS SKiKP

sPP

P S K I J c i p s LR LQ define each

what does recoding teh arrival times of siesmic waves tell us about the internal structure of the earth

earth is not uniform

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Pwave shadow zone-low velocity outer core

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swave shadow zone-liquid outer core

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forward and invers modlign of travel times give us a radial siemic velityu modle of the earth