Globale Seismizität II Spannungsfeld Seismotektonik Literatur: Berckhemer, H., Grundlagen der Geophysik, Wiss. Buchges. 1990. Stüwe, K. Geodynamik der Lithospäre, Springer, 2000 Sheaer, P., Introduction to Seismology, Cambridge University Press, 1999. Lay, T. & T. Wallace, Modern Global Seismology, Academic Press, 1995.
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Globale Seismizität II Seismotektonik · Globale Seismizität II Spannungsfeld Seismotektonik Literatur: Berckhemer, H., Grundlagen der Geophysik, Wiss. Buchges. 1990. Stüwe, K.
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Globale Seismizität II
SpannungsfeldSeismotektonik
Literatur:Berckhemer, H., Grundlagen der Geophysik, Wiss. Buchges. 1990. Stüwe, K. Geodynamik der Lithospäre, Springer, 2000
Sheaer, P., Introduction to Seismology, Cambridge University Press, 1999.
Lay, T. & T. Wallace, Modern Global Seismology, Academic Press, 1995.
2
Wiederholung
3
+
+ -
-
first motiontoward focus
first motionaway from focus
- dilatation+ compression
Wavetype: P-waves (+ and - first motion)
On nodal planes sign reversal no displacement
P-wave motion equal for 2 conjugate faults (fault plane and auxiliary plane)
Source deformation
4
Influence of shear on an infinitesimal volume
A B
C D
Volume element
A´B´
C´D´
Shear parallel to sides BD, AC
A'D' is extendedB'C' is compressed
Equal value of relative change in length but different signs
PT
5
Radiation from Double couplehorizontal or vertical shear source
Double Couple P
-1-0.5
00.5
1S- N-1
-0.5
0
0.5
1
W- E-1
-0.5
0
0.5
1
Z
-1-0.5
00.5
1S- N
Doublee Couple S
-1-0.5
00.5
1S- N-1
-0.5
0
0.5
1
W- E-1
-0.5
0
0.5
1
Z
-1-0.5
00.5
1S- NParticle motion due to the wave
Rupture: displacement across the fault
P waves: 4 lobes, 2 nodal planes
S waves:2 nodal lines
P
PT
T
6
Radiation from Double couplehorizontal or vertical shear source
Double Couple P
-1-0.5
00.5
1S- N-1
-0.5
0
0.5
1
W- E-1
-0.5
0
0.5
1
Z
-1-0.5
00.5
1S- N
Doublee Couple S
-1-0.5
00.5
1S- N-1
-0.5
0
0.5
1
W- E-1
-0.5
0
0.5
1
Z
-1-0.5
00.5
1S- N
P waves: 4 lobes, 2 nodal planes
S waves:2 nodal lines
P
PT
T
Symmetric radiation from source: cannot distuingish fault plane and auxiliary plane
7
Fault-Plane solutionsP- and T-axes= directions of maximal compres-sion/extension in radiation pattern
Generally P, T NOT equal tectonic stress axes, only under 45° - hypothesis
e.g. San-Andreas fault: max. principal stress ┴ fault
8
Point source - shear dislocationDefinition of strike, dip, slip(Streichen, Fallen, Neigung)
Strike
Dip Rake
Rupture surface A0
0 Φ 360 °<≤0 δ 90 °≤ ≤
180° λ 180 °≤<–
9
σ11
σ12σ13
σ21
σ22σ23
σ31
σ32
σ33
x1
x2
x3
Meaning of :σijσij= force in j direction on
an area whose normal points to i direction
=> Stress vector on each area with normal i:
Ti( )
T1i( ) T2
i( ) T3i( ), ,( ) σi1 σi2 σi3, ,( )= =
10
Shear stress τ on arbitray plane?
1σ
3σ
Shear Stress τ on this plane?Angle θ of rupture?
θ
11
Rupture plane and Mohr circle
nσ
τ
1σ3σ ( )1 3 / 2σ σ+
0crit nτ τ µ σ= +θµ
2θ
Real materials do not rupture under 45° to σ1!θ depends on μ, normally θ≈30°
12
NF: Normal faulting
NS: Predominately normal with strike-slip component
TF: Thrust faulting
TS: Predominately thrust with strike-slip component
SS: Strike-slip faulting (includes minor normal or thrust component)
Fault types & stress regimes
If Coulomb criterium applies: first estimate stress field from fault-plane solution dependent on coefficient of internal friction.
13
B World Stress Map Projekt
Compilation of the global stress field, SHmax directions