
What magnitude was the Oklahoma Earthquake?
4.3 (Mw) moment magnitude per USGS
5.1 magnitude (mbLg) by Oklahoma Geological Survey

Why is there discrepancy between measurements of the Norman earthquake?
Different measurement surveys, USGS vs. Oklahoma Geological Survey

Nst
Number of seismic stations which reported P and Sarrival times for the EQ

Nph
Number of P and Sarrival time observations used to compute the hypocenter location

Dmin
Horizontal distance from the epicenter to the nearest station (in km)

Rmss
The rootmeansquare (RMS) travel time residual, in sec

Gp
The largest azimuthal gap between azimuthally adjacent stations (in degrees)


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

Date and time of the EQ (epicenter)
October 13, 2010. 9:06am

Epicenter location distance from Norman
10 miles East



Epicenter definition
the point on the Earth's surface vertically above the hypocenter

Hypocenter definition
the point in the crust where a seismic rupture actually occurs

Area of the earth from angular distances of ___ to ___ degrees from a given EQ that does not receive any direct ____ waves
Pwave shadow zone; 103, 144, P.

The shadow zone results from
S waves being stopped entirely by the liquid core and P waves being bent (refracted) by the liquid core

Shadow zone  Swaves being
stopped entirely by the liquid core

Shadow zone  Pwaves being
bent (refracted) by the liquid core

EQs near OKC
Jones Earthquake Swarm area

Location of greatest number of EQs in OK
Eastern Oklahoma county, near Jones, OK

Largest EQ in Oklahoma
 Magnitude 5.5 (intensity XII)
 Occurred April 9, 1952
 centered near El Reno

Largest OK earthquake caused by slippage along
Nemaha fault

Second largest earthquake in OK magnitude and location
Magnitude 4.6, near Wewoka

Third largest earthquake in OK magnitude and location
4.3 magnitude, 10 miles east of Norman

Is there any obvious reasons why the earthquake was located there?
Oklahoma basins

Rock age at hypocenter of OK EQ
Precambrian

mathematical device to compare the size of earthquakes
Richter scale

The magnitude from an earthquake is determined from
the logarithm of the amplitude of waves recorded by seismographs

Because of the logarithmic basis of the scale, each whole number increase in magnitude represents
a tenfold increase in measured amplitude

Difference in measured energy between each whole number on the Richter scale
31 times more energy than previous whole number

Earthquakes with magnitude 2.0 or less called
microearthquakes

Great earthquakes have magnitude of
8 or greater

True of false: The Richter scale has no upper limit.
True

Another scale devised for more precise study of great earthquakes
moment magnitude scale

True of false: the Richter scale is used to express damage.
False

An estimate of the energy release or size of an earthquake
Magnitude (M)

________ a measure of the size of the earthquake.
________ is the level of ground shaking at a specific location
Magnitude
Intensity

Earthquake Magnitude  Various Scales
ML
local magnitude consistent with the magnitude of Richter

Earthquake Magnitude  Various Scales
Mw
Moment Magnitude

Earthquake Magnitude  Various Scales
MS
teleseismic surfacewave magnitudes at period of ~ 20 sec

Earthquake Magnitude  Various Scales
mb(Lg)
regional Lg magnitude measured in a narrow period range around 1s
determined from 1.0 hertz S waves

Magnitude (M) is controlled by
the fault length (or area) that ruptures

What controls the level of shaking in an earthquake?
Magnitude more energy released
Distance shaking decays with distance
Local soils amplify the shaking

Bigger earthquakes last a _____ time
longer

MMI =
Modified Mercalli Intensity

Largest recorded earthquake in the world was a magnitude ___ located in ___ on _____.
9.5, Chile, May 22, 1960

Largest recorded earthquake in the US magnitude ____ in _____ on _____.
9.2, Alaska, Good Friday, 1964

How many detectable earthquakes in the world each year?
500,000

Most earthquake waves have a frequency of
less than 20 Hz

In the US, which two states have the smallest number of earthquakes?
Florida and North Dakota

Mid Continent Rift and New Madrid Area contain two types of faults
strike slip
reverse fault

