Mechanics of Earthquakes and Faulting

1
Mechanics of Earthquakes and Faulting
23 Feb. 2007
Friction, Mechanics of Faulting

• Rate-state friction
• Healing data Stick-slip stress drop(V), ??(t,
  V, ?)
• Repeating Earthquakes
• Andersons Theory of Faulting
• Seismological and Structural Evolution of
  Faulting

2
Time dependent yield strength
Dieterich and Kilgore 1994
Time dependent growth of contact (acyrlic
plastic)- true static contact
3
Load point
Fault surface
4
Stressed Aging Aging rate depends on the rate of
shearing
(Marone, 1998, Nature)
5
Earthquake stress-drop is higher for lower
loading rates (longer inter-event time). This is
an example of Fault Healing.
6
Friction, Restrengthening How do faults regain
strength between earthquakes? Interplate vs.
Intraplate Events Stress Drop as a function of
avg. recurrence interval.
See Scholz, Sec 6.3
7
Peng, Vidale, Marone, Rubin, 2005 GRL. Variations
in moment with recurrence interval of repeating
aftershocks of the 1984 Morgan Hill, California,
earthquake
8
Vidale, Ellsworth, Cole, Marone, Nature, 1994
Jan80 26Apr84 29Apr84 3May84 12May84 27May84 June8
4 Jul84 Sep84 Nov84 Nov84 Oct85 Jun86 Feb87 May87
Jul88 Jan90 Sep91
0
2
4
6
8
10
Seconds, Station HCA for CA1 sequence
9
Vidale, Ellsworth, Cole, Marone, Nature, 1994
10
N
M6.2 1984 M.H. Rupture
CA1 Repeating Sequence
M 1.5 z 6 km Mo 5.5x1011 Nm ?d 0.025 s r
40 m ?? 4.5 MPa
11
Earthquake stress-drop is higher for lower
loading rates (longer inter-event time). This is
an example of Fault Healing.
12
The rate of frictional healing depends on the
rate of shearing (Quartz gouge. Marone, 1998,
Nature) Rate State Friction Laws predict this
behavior
13

• Fault slip rate varies during the seismic cycle
  (coseismic, afterslip, interseismic)
• Average shear stress level varies throughout the
  seismic cycle
• The rate of frictional healing depends on the
  rate of shearing

14
(No Transcript)
15

• Assuming
• Lab values for friction parameters a and b
• Lab Field-based estimate of Dc
• Dc proportional to shear zone width
• Stiffness k G/r

16

• Assuming
• Lab values for friction parameters a and b
• Lab Field-based estimate of Dc
• Dc proportional to shear zone width
• Stiffness k G/r

17

• Andersons Theory of Faulting
• Free Surface and Principal Stresses

18

• Three Modes of Faulting

19
Fault Growth and Development