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What magnitude was the Oklahoma Earthquake?
4.3 (Mw) moment magnitude per USGS
5.1 magnitude (mbLg) by Oklahoma Geological Survey
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Why is there discrepancy between measurements of the Norman earthquake?
Different measurement surveys, USGS vs. Oklahoma Geological Survey
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Nst
Number of seismic stations which reported P- and S-arrival times for the EQ
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Nph
Number of P- and S-arrival time observations used to compute the hypocenter location
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Dmin
Horizontal distance from the epicenter to the nearest station (in km)
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Rmss
The root-mean-square (RMS) travel time residual, in sec
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Gp
The largest azimuthal gap between azimuthally adjacent stations (in degrees)
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Moment (mW)
Based on the moment of the EQ. Rigidity of the Earth times the average amount of slip on the fault times the amount of fault area that slipped
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Date and time of the EQ (epicenter)
October 13, 2010. 9:06am
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Epicenter location distance from Norman
10 miles East
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Epicenter definition
the point on the Earth's surface vertically above the hypocenter
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Hypocenter definition
the point in the crust where a seismic rupture actually occurs
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Area of the earth from angular distances of ___ to ___ degrees from a given EQ that does not receive any direct ____ waves
P-wave shadow zone; 103, 144, P.
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The shadow zone results from
S waves being stopped entirely by the liquid core and P waves being bent (refracted) by the liquid core
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Shadow zone - S-waves being
stopped entirely by the liquid core
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Shadow zone - P-waves being
bent (refracted) by the liquid core
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EQs near OKC
Jones Earthquake Swarm area
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Location of greatest number of EQs in OK
Eastern Oklahoma county, near Jones, OK
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Largest EQ in Oklahoma
- Magnitude 5.5 (intensity XII)
- Occurred April 9, 1952
- centered near El Reno
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Largest OK earthquake caused by slippage along
Nemaha fault
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Second largest earthquake in OK magnitude and location
Magnitude 4.6, near Wewoka
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Third largest earthquake in OK magnitude and location
4.3 magnitude, 10 miles east of Norman
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Is there any obvious reasons why the earthquake was located there?
Oklahoma basins
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Rock age at hypocenter of OK EQ
Precambrian
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mathematical device to compare the size of earthquakes
Richter scale
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The magnitude from an earthquake is determined from
the logarithm of the amplitude of waves recorded by seismographs
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Because of the logarithmic basis of the scale, each whole number increase in magnitude represents
a tenfold increase in measured amplitude
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Difference in measured energy between each whole number on the Richter scale
31 times more energy than previous whole number
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Earthquakes with magnitude 2.0 or less called
microearthquakes
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Great earthquakes have magnitude of
8 or greater
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True of false: The Richter scale has no upper limit.
True
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Another scale devised for more precise study of great earthquakes
moment magnitude scale
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True of false: the Richter scale is used to express damage.
False
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An estimate of the energy release or size of an earthquake
Magnitude (M)
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________ a measure of the size of the earthquake.
________ is the level of ground shaking at a specific location
Magnitude
Intensity
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Earthquake Magnitude - Various Scales
ML
local magnitude consistent with the magnitude of Richter
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Earthquake Magnitude - Various Scales
Mw
Moment Magnitude
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Earthquake Magnitude - Various Scales
MS
teleseismic surface-wave magnitudes at period of ~ 20 sec
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Earthquake Magnitude - Various Scales
mb(Lg)
regional Lg magnitude measured in a narrow period range around 1s
determined from 1.0 hertz S waves
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Magnitude (M) is controlled by
the fault length (or area) that ruptures
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What controls the level of shaking in an earthquake?
Magnitude -more energy released
Distance -shaking decays with distance
Local soils -amplify the shaking
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Bigger earthquakes last a _____ time
longer
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MMI =
Modified Mercalli Intensity
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Largest recorded earthquake in the world was a magnitude ___ located in ___ on _____.
9.5, Chile, May 22, 1960
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Largest recorded earthquake in the US magnitude ____ in _____ on _____.
9.2, Alaska, Good Friday, 1964
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How many detectable earthquakes in the world each year?
500,000
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Most earthquake waves have a frequency of
less than 20 Hz
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In the US, which two states have the smallest number of earthquakes?
Florida and North Dakota
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Mid Continent Rift and New Madrid Area contain two types of faults
strike slip
reverse fault
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