bill ellsworth u.s. geological survey near-source observations of earthquakes: implications for...
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Bill Ellsworth
U.S. Geological Survey
Near-Source Observations of Earthquakes:Implications for Earthquake Rupture and Fault
Mechanics
JAMSTEC International Technical Committee on Long Term Monitoring System Development for Ocean Boreholes
Yokohama, Japan February 16-17, 2009
A central goal of seismology is to understand the physical conditions under which earthquakes occur
Key question seismology can address inthe near-source region include:
• Minimum size of earthquakes• Magnitude dependence of source parameters• Rupture nucleation• Stress evolution during and following rupture
rD
Illustrations by Peter Shearer
A central goal of seismology is to understand the physical conditions under which earthquakes occur
Key question seismology can address inthe near-source region include:
• Minimum size of earthquakes• Magnitude dependence of source parameters• Rupture nucleation• Stress evolution during and following rupture
u(t).
σd
Dc
ES
A central goal of seismology is to understand the physical conditions under which earthquakes occur
Key question seismology can address inthe near-source region include:
• Minimum size of earthquakes• Magnitude dependence of source parameters• Rupture nucleation• Stress evolution during and following rupture
.
σd
Dc
ES
Shaking Forecast Model
World-wide Strong Motion Data Set(as of 2004)
2002 M 7.9Denali Earthquake
Near-Field Ground Motion at
Pump Station 10
East (km)
Nort
h (
km)
-20 -10 0 10 20
-20
-10
010
20
1 m
Accelerations were modest (0.36 g)Acc
ele
ration
(cm
/sec^
2)
-300
-100
100
300
Acc
ele
ration
(cm
/sec^
2)
-300
-100
100
300
Seconds
Acc
ele
ration
(cm
/sec^
2)
-300
-100
100
300
0 20 40 60 80
Fault Normal
Fault Parallel
Vertical
Velo
city
(cm
/s)
-100
050
100
200
Velo
city
(cm
/s)
-100
050
100
200
Seconds
Velo
city
(cm
/s)
-100
050
100
200
0 20 40 60 80
Velocities were pulse-like (180 cm/s)
East (cm/s)
Nort
h (
cm/s
)
-100 -50 0 50 100 150 200
-15
0-1
00
-50
050
100
150
1718
1920
21
22 2324
25
Fault Normal
Fault Parallel
Vertical
Displacements were geodetic (2.8 m)
Dis
pla
cem
en
t(cm
)
-20
0-1
00
01
00
20
0
Dis
pla
cem
en
t(cm
)
01
00
20
03
00
Seconds
Dis
pla
cem
en
t(cm
)
-10
00
10
02
00
30
0
0 20 40 60 80
East (cm)
Nort
h (
cm)
0 100 200 300
-20
0-1
00
01
00
200
17 18
1920
21
22
2324
25
Fault Normal
Fault Parallel
Vertical
Where Does the Energy Come From?
Isochrones and Fault Parallel Displacement Intensity for Pump Station 10
0 . 00
0 . 05
0 . 10
0 . 15
0 . 20
0 . 25
* 1 0 * *0
- 60 - 40 - 20 0 20 40
DISTANCE ALONG STRIKE, KM
2.0
4.0
6.0
8.0
10
.0D
ISTA
NC
E D
OW
N D
IP,
KM
- 60 - 40 - 20 0 20 40
DISTANCE ALONG STRIKE, KM
2.0
4.0
6.0
8.0
10
.0D
ISTA
NC
E D
OW
N D
IP,
KM
30 .
30 .
30 .
35 .
35 .
35 .
40 .
40 .
40 .
45 .
45 .
45 .
50 .
50 .
50 .
55 .
55 .
55 .
60 .
60 .
60 .
65 .
65 .
65 .
0 . 0
0 . 1
0 . 2
0 . 3
0 . 4
0 . 5
0 . 6
* 1 0 * *0
- 60 - 40 - 20 0 20 40
DISTANCE ALONG STRIKE, KM
2.0
4.0
6.0
8.0
10
.0D
ISTA
NC
E D
OW
N D
IP,
KM
- 60 - 40 - 20 0 20 40
DISTANCE ALONG STRIKE, KM
2.0
4.0
6.0
8.0
10
.0D
ISTA
NC
E D
OW
N D
IP,
KM
30 .
30 .
30 .
35 .
35 .
35 .
35 .
40 .
40 .
40 .
45 .
45 .
45 .
50 .
50 .
50 .
55 .
55 .
55 .
60 .
60 .
60 .
Note change in scale
How high are the stresses that cause big earthquakes?
San Andreas Fault Observatory at Depth(SAFOD)
Increase in Least Principal Stress Observed in the San Andreas Fault Zone
SAFOD
Stress Magnitudes: Pilot Hole, SAFOD
SV
Lithostat
SAFOD Seismic SensorsCommercial high-frequency borehole seismometers
(Oyo Geospace DS150 – 150 C rating)
MEMS accelerometers replace geophones for broad band response
Static Stress Drop Measurements at SAFOD
Hickman & Zoback (2004)
Average value is near the strength of the rock.
Parkfield MainshockObserved on the Pilot Hole Array
2 seconds
P
S
2004 Parkfield Main Shock and Early Aftershocks
4 Minutes of Aftershocks of 2004 Parkfield Earthquake
World-wide Strong Motion Data Set(as of 2004)
World-wide Strong Motion Data Set(as of 2004)
NanTroSEIZE?