Geol 600 Notable Historical Earthquakes

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• Geol 600 Notable Historical Earthquakes
• Finite fault rupture propagation
• http//www-rohan.sdsu.edu/kbolsen/geol600_nhe_sou
  rce_inversion.ppt

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9 Force Couples Mij (the moment tensor), 6
different (MijMji). Mfd
M11 M12 M13 Good approximation for
distant M M21 M22 M23 earthquakes due to
a point source M31 M32 M33 Larger
earthquakes can be modeled
as sum of point sources
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Description of earthquakes using moment tensors
Parameters strike ?, dip ?, rake
? Right-lateral ?180o, left-lateral ?0o, ?90
reverse, ?-90 normal faulting Strike, dip, rake,
slip define the focal mechanism
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Description of earthquakes using moment tensors
M11 -M0(sin? cos? sin2?s sin2? sin?
sin2?s), M12 M0(sin? cos? cos2?s 0.5 sin2?
sin? sin2?s), M13 -M0(cos? cos? cos?s cos2?
sin? sin?s), M22 M0(sin? cos? sin2?s - sin2?
sin? cos2?s), M23 -M0(cos? cos? sin?s - cos2?
sin? cos?s), M33 M0 sin2? sin??
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P-waves S-waves
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Finite-size Fault PlaneDivide into sub-faults
x x x x x
x x x x x x
x x x x x x
x x x x
x x x x x x
x x x x x x
x x x x x
x x
sub-faults
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Define rupture parameters (distributions of slip,
rake, rupture speed, source-time function,
stress, friction, etc) wave-propagation
code Compute synthetic seismograms at receiver
locations Compare synthetic to observed
seismograms Synthetics fit
data? Yes

no
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Kinematic source inversion Solves for slip
history on the fault Dynamic source
inversion Solves for stress and friction on the
fault

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Kinematic Source Inversion
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Landers Classic Vertical Strike-Slip Event
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Test case1992 M 7.3 Landers
Well-recorded event
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Slip-weakening Rupture Model
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Dynamic Rupture From Trial-and-Error
Finite-Difference Modeling

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How is rupture propagation affected by
realistic variation of dynamic parameters?Lets
look at changes in the stress drop
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Inverted (Trial-and-Error) Dynamic Radiation
Versus Data

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Stress Field (a)
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Stress Field (b)
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Stress Field (c)
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1994 M6.7 Northridge
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1994 M6.7 Northridge
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2004 M6.0 Parkfield
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2004 M6.0 Parkfield
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1999 M7.4 Izmit
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SOURCE TIME FUNCTION DURATION ALSO VARIES WITH
STATION AZIMUTH FROM FAULT. THIS DIRECTIVITY CAN
CONSTRAIN WHICH NODAL PLANE IS THE FAULT PLANE
Directivity similar to Doppler Shift, but differs
in requiring finite source dimension
Stein Wysession, 2003
For earthquake, V/VR 1.2 for shear waves and 2.2
for P waves. Maximum duration is 180 from the
rupture direction, and the minimum is in the
rupture direction. Analogous effect thunder
generated by sudden heating of air along a
lightning channel in the atmosphere. Here V/VR
0, so observers perpendicular to the channel
hear a brief, loud, thunder clap, whereas
observers in the channel direction hear a
prolonged rumble.