Earthquake Seismology for
Tsunami Warning:
Nomenclature, Faulting, Magnitude
Masahiro Yamamoto
UNESCO/IOC
Laura Kong
ITIC
Walter Mooney
USGS
How does a seismometer work?
A simple seismometer
Magnetic Tape Record
Analog Record
An observatoryclass
seismometer
Streckeisen STS-1 Very Broadband Seismometer
High frequency
seismometers
Streckeisen STS-2
Guralp CMG-3T
Teledyne GS-13
Short period sensors do not record long period signals
Seismogram showing different phases
Earthquake Nomenclature
Described by Time (t) and Location (x,y,z)
Hypocenter (Focus):
Origin Time,
Latitude, Longitude,
Depth
Location in Earth where
energy in the rock being
strained is released
Epicenter:
Latitude, Longitude
Point on Earth’s surface
directly above
Hypocenter
Hypocenter
EARTHQUAKE CLASSIFICATION
MAGNITUDE
CLASSIFICATION
M ≥ 9.0
Gigantic (? new term)
M ≥ 8.0
Great Earthquake
7.0 < M < 8.0
Major / Large Earthquake
5.0 < M < 7.0
Moderate Earthquake
3.0 <M < 5.0
Small Earthquake
1.0 < M < 3.0
Microearthquake
M < 1.0
Ultra Microearthquake
Hagiwara, 1964
TYPES OF EARTHQUAKES
1) Tectonic Earthquake – MOST COMMON (FAULTS)
2) Volcanic Earthquake
3) Collapse Earthquake
4) Explosion Earthquake
CLASSIFICATION
DISTANCE
1) Teleseismic Earthquake
> 1000 km
2) Regional Earthquake
> 500 km
3) Local Earthquake
< 500 km
北朝鮮
地下核実験
牡丹江（３８０ｋｍ）
振幅が次第に大きくなってきている
2009と2013の比較
Types of faults
Normal
fault
Thrust (Reverse) fault
Strike-slip fault
Tsunami by Earthquake
Earthquake Magnitude
M7, PNG earthquake
Decay of amplitude
Epicentral distance
32 times
1,000 times
EARTHQUAKE ENERGY
log E = 12 + 1.8 ML
log E = 5.8 + 2.4 mb
log E = 11.4 + 1.5 Ms
Magnitude versus ground motion and energy
Magnitude
Ground Motion
1.0
0.5
0.3
0.1
10.0 times
3.2 times
2.0 times
1.3 times
Energy
about 32 times
about 5.5 times
about 3 times
about 1.4 times
Earthquake Magnitude and Tsunami
Ground
Magnitude
Displacement(m)
Length
(km)
3
4
5
6
7
8
9
～0.03
～0.08
～0.25
～0.8
～2.5
～8
～25
～0.4
～1.4
～4
～14
～40
～140
～450
Length
M:+1→Displacement×3, Length×3
Richter Scale = Magnitude
Types of Magnitude Scales
Period Range
ML
Local magnitude (California)
Mj
JMA (Japan Meteorol. Agency) regional S & surface waves 5-10 sec
mb Body wave magnitude
Ms
Surface wave magnitude
Mwp P-wave moment magnitude
regional S & surface waves 0.1-1 sec
teleseismic P waves
1-5 sec
teleseismic surface waves
20 sec
teleseismic P waves
10-60 sec
Mw
Moment magnitude
teleseismic surface waves
> 200 sec
Mm
Mantle magnitude
teleseismic surface waves
> 200 sec
Ref: USGS Seismology and Tsunami Warnings, 2006 (Earthquake Source)
Saturation
• Ml, Ms and mb all suffer from saturation.
• Occurs for 2 reasons:
Time window saturation:
Magnitude is calculated for time
window that is less than
duration of rupture
(particularly affects mb)
Spectral saturation:
Wavelength of wave too short to
“see” all of rupture
(affects mb, Ml, and Ms)
Kanamori 1983
Magnitude and Intensity
M:8.0
M: 9.0
2011 Tohoku Earthquake 2003 Off-Tokachi EQ
LP records
Thank You
Masahiro Yamamoto
UNESCO/IOC
Earthquake size - Seismic Moment, M0
Mechanical measure of EQ size
Mathematically, how big an area and how far fault moves.
15 km
10
Area (A)
Slip (S),
displacement
5
Seismic Moment = (Rigidity)(Area)(Slip)
M 0 (t ) = µ ⋅ S ⋅ ∆u (t )
Mw=2/3logMo – 10.7
0
M4 M5 M6
Seismic moments and fault areas
of some famous earthquakes
2004 Sumatra
400
9.3
3-Component Seismograms of an aftershock of the 2004 Sumatra Earthquake
Identification of phases: P-wave = vertical component, S-wave = horizontal