Download Lithosphere structure of Central Asia and Tien Shan

Lithosphere structure of Central Asia and
Tien Shan
Keith Priestley
Bullard Laboratories, Department of Earth Sciences, University of Cambridge
Earthquake Science and Hazard in Central Asia
Almaty, Kazakhstan – 7 September 2016
Lithospheric structure of Central Asia
and the Tien Shan
Keith Priestley
Almaty, Kazakhstan −− 7 September 2016
overview – main points of this talk
I
The LITHOSPHERE is the solid, rigid, brittle outer
part of the Earth overlying the plastic, ductile,
mechanically-weak ASTHENOSPHERE.
overview – main points of this talk
I
The LITHOSPHERE is the solid, rigid, brittle outer
part of the Earth overlying the plastic, ductile,
mechanically-weak ASTHENOSPHERE.
I
There are large variations in the lithospheric
thickness of Central Asia.
overview – main points of this talk
I
The LITHOSPHERE is the solid, rigid, brittle outer
part of the Earth overlying the plastic, ductile,
mechanically-weak ASTHENOSPHERE.
I
There are large variations in the lithospheric
thickness of Central Asia.
I
The nature of the lithosphere controls the size of felt
ground motion area and the large-scale processes
affecting the structure of the Earth’s crust.
overview of talk
I
What is the lithosphere?
overview of talk
I
What is the lithosphere?
I
Locating the lithosphere-asthenosphere
boundary
overview of talk
I
What is the lithosphere?
I
Locating the lithosphere-asthenosphere
boundary
I
Variations in the lithospheric thickness of
Central Asia
overview of talk
I
What is the lithosphere?
I
Locating the lithosphere-asthenosphere
boundary
I
Variations in the lithospheric thickness of
Central Asia
I
Influence of the lithosphere on earthquakes
What is the lithosphere?
The strong, rigid, brittle outer layer of the Earth
lithosphere
asthenosphere
The lithosphere includes the crust and uppermost mantle.
What is the lithosphere?
The strong, rigid, brittle outer layer of the Earth
rigid
plastic
The lithosphere includes the crust and uppermost mantle.
Locating the lithosphere-asthenosphere boundary
Proxies for the lithosphere-asthenosphere boundary
The lithosphere-asthenosphere boundary (LAB) coincides
with the depth in the upper mantle where the response of
materials to forces changes from brittle to plastic. This is
primarily controlled by the increase of temperature with depth.
wave speed
anisotropy
strain rate
resistivity
temperature
conducting
depth
resistive
various
definitions
change in
anisotropy
LAB
rigid
LAB
LAB
LAB
deforming
conducting
convecting
adapted from
Eaton et al (2009)
Locating the lithosphere-asthenosphere boundary
seismic surface waves
Locating the lithosphere-asthenosphere boundary
seismic body waves
Locating the lithosphere-asthenosphere boundary
seismic receiver functions
Locating the lithosphere-asthenosphere boundary
seismic anisotropy
Locating the lithosphere-asthenosphere boundary
electrical resistivity
Locating the lithosphere-asthenosphere boundary
petrology
Locating the lithosphere-asthenosphere boundary
temperature vs. depth in the continents
Steady−state continental geotherm
surface heat
flux 51.2 mW/m 2
flux 12.4 mW/m 2
Crust
constant heat production
granulite composition
constant conductivity
Mechanical boundary layer
Mantle
conductivity = f(T)
no heat production
Base of lithosphere
226 km
Thermal boundary layer
Isentropic interior
Tp = 1315o C
Locating the lithosphere-asthenosphere boundary
seismic wave paths
body waves
P
surface waves
S
SKS
Fundamental
mode
higher
modes
500
1000
1500
2000
seconds after origin time
2500
3000
surface waves
seismograph
earthquake
P,S
SKS
mantle
outer
core
core−mantle
boundary
surface
Locating the lithosphere-asthenosphere boundary
seismic structure of the Pacific Ocean
A
40.000 N, 120.000 E
A’
-33.336 S, 83.605 W
Japan
Hawaii
Depth / km
A
A
B’
B’
4000
2000
0
EPR
0
100
200
300
400
C’
C’
0
B
10
20
30
40
50
60
70
80
90
100
110
120
-25.000 S, 156.000 E
130
140 150 160
B’
38.185 N, 123.868 W
4000
2000
0
Hawaii
Vanuatu
Depth / km
0
B
B
100
200
300
C
C
400
A’
A’
0
C
10
20
30
40
50
60
70
-30.000 S, 160.000 E
Tonga
Depth / km
0
75 km
80
90
C’
15.350 N, 79.263 W
EPR
Central
America
100
200
300
δ VS (%)
VS ref = 4.408 km/s
400
0
-9
-6
-3
0
3
6
9
10
20
30
40
50
60
70
Distance / degrees
80
90
100
110
120
4000
2000
0
Locating the lithosphere-asthenosphere boundary
Relationship between shear wave speed and seafloor age
Locating the lithosphere-asthenosphere boundary
Relationship between shear wave speed and temperature
(b)
depth (km)
shear wave speed vs seafloor age
100
200
300
400
25
50
75
100
125
plate temperature vs seafloor age
20
500C
60
1000C
100
25
150
50
age (mya)
4.0 4.2 4.4 4.6 4.8 5.0
shear wave speed (km/s)
(c)
4.7
4.6
shear wavespeed (km/s)
depth (km)
(a)
4.5
4.4
4.3
50 km
4.2
75 km
4.1
600
800
1000
temperature (C)
1200
100
75
age (mya)
125
150
Locating the lithosphere-asthenosphere boundary
seismic estimates of the continental geotherm
temperature (oC)
400
800 1200 1600
s
idu
100
gr
di aph
am it
on e
d
temperature (oC)
400
800 1200
0
sol
depth (km)
0
100
MBL
TBL
(a)
179 km
175 km
isentropic
200
200
300
(b)
Variations in the lithospheric thickness of Central Asia
Eastern Asia – topography, seismicity, lithosphere
topography and earthquakes
lithospheric thickness and earthquakes
55˚
55˚
Siberian
Shield
East
European
Craton
180
160
50˚
200
160
240
50˚
220
220
210
190
45˚
180
180
45˚
Tien Shan
160
190
40˚
Tarim
Basin
100
140
100
40˚
100
160
100
North
China
Craton
210
35˚
275
35˚
160
100
10
0
30˚
Tibet
30˚
140
275
25˚ 100
180
140
230
210
South
China
Craton
210
25˚
18
0
190
20˚
160
20˚
15˚
15˚
140
140
140
100
10˚
100
5˚
Lithospheric thickness (km)
100 120 140 160 180 200 220 240 260
110˚
100˚
90˚
80˚
10˚
70˚
South
Indian
Shield
Variations in the lithospheric thickness of Central Asia
Tien Shan – topography, seismicity, lithosphere
lithospheric thickness and earthquakes
160
180
topography and earthquakes
160
45˚
0
19
45˚
100
100
140
100
18
0
40˚
230
40˚
190
0
20
210
180
16
240
70˚
275
80˚
90˚
Lithospheric thickness (km)
100 120 140 160 180 200 220 240 260
0
100
275
35˚
Variations in the lithospheric thickness of Central Asia
Baikal Rift – topography, seismicity, lithosphere
topography and earthquakes
lithospheric thickness and earthquakes
60˚
60˚
200
Siberian Craton
Siberian Craton
200
0
21
220
160
55˚
200
0
55˚
160
16
180
140
100
50˚
50˚
180
160
45˚
45˚
10
0
100
180
200
140
40˚
100
90˚
100˚
110˚
120˚
Lithospheric thickness (km)
100 120 140 160 180 200 220 240 260
130˚
Influence of the lithosphere on earthquakes
North America – comparison of felt areas
topography and earthquakes
lithospheric thickness and earthquakes
50˚
50˚
50˚
230
50˚
19
45˚
40˚
35˚
35˚
New Madrid
1811 −− M 7.5
100
San Francisco
1906 −− M 7.8
Charleston
1886 −− M 7.3
180
30˚
30˚
30˚
35˚
0
35˚
40˚
100
100
20
40˚
45˚
20
0
40˚
0
210
45˚
45˚
30˚
160
140
160
25˚
25˚
25˚
25˚
Modified Mercalli Intensity 140 V
20˚
100
100
−100˚
−110˚
−120˚
−100˚
−120˚
0
2000 4000 6000 8000
−80˚
topography (m)
−6000 −4000 −2000
−90˚
−80˚
−90˚
−110˚
100
Lithospheric thickness (km)
100 120 140 160 180 200 220 240 260
Comparison of felt areas (Modified Mercalli Intensity Scale V )
for similar magnitude earthqauakes. The felt area is strongly
affected by the presence of the thick lithosphere.
20˚
Influence of the lithosphere on earthquakes
different tectonic settings
shortening
rifting
(Tien Shan)
(Baikal)
Summary – main points of this talk
I
The LITHOSPHERE is the solid, rigid, brittle outer
part of the Earth overlying the plastic, ductile,
mechanically-weak ASTHENOSPHERE.
Summary – main points of this talk
I
The LITHOSPHERE is the solid, rigid, brittle outer
part of the Earth overlying the plastic, ductile,
mechanically-weak ASTHENOSPHERE.
I
There are large variations in the lithospheric
thickness of Central Asia.
Summary – main points of this talk
I
The LITHOSPHERE is the solid, rigid, brittle outer
part of the Earth overlying the plastic, ductile,
mechanically-weak ASTHENOSPHERE.
I
There are large variations in the lithospheric
thickness of Central Asia.
I
The nature of the lithosphere controls the size of felt
ground motion area and the large-scale processes
affecting the structure of the Earth’s crust.