Download Laboratory experiments

Magnitude of Earthquake
A
M  log 10 ( )  q( , h )  a
T
A: maximum amplitude of the wave in μm
T: Period of the wave in second
q: Function correcting for the decrease of
amplitude of the wave with the distance
from epicenter and focal depth
Δ:Angular distance
h: focal depth
a: empirical constant
Gutenberg-Richter Scale (1956)
A
mb  log 10 ( ) max  q( , h )
T
For Shallow Focus (<50Km),
Teleseismic Earthquake
(20o<Δ<160o)
A
M s  log 10 ( ) max  1.66 log 10   3.3
T
A
mb  log 10 ( )  0.01  5.9
12
 mb= 2.87 + 0.60 Ms for nuclear explosions
 Ms= 1.68 mb - 4.82 for earthquakes
The mb:Ms data plots vary appreciably from
one earthquake region to the next, a
worldwide average of mb:Ms relations is
mb=2.94 + 0.55 Ms
Two magnitude scales coincide at
magnitude 6.5
For small magnitudes
mb > Ms
For large magnitudes
mb < Ms
The moment magnitude Mw
The seismic moment Mo of an earthquake
is defined by
Mo=μAu
μ : the shear modulus
A : the area of the fault
u : the average displacement on the fault
Mw=(2/3)log10Mo – 6.0
Magnitude – Frequency Relation
log N = constant – bMs
N Frequency of the quakes
b≈1 an approximate worldwide average
Laboratory experiments
High stress results in low values of b
Low stress results in high values of b
The Relation between Energy
and Magnitude used by Båth
(1966)
Log10E = 5.24 + 1.44 Ms
.2008-06-地震報告;地震測報分析