1 scec, usc ; 2 university of wyoming ; 3 sripps , ucsd ;...
TRANSCRIPT
Full-3D Tomography of the Crustal Structure in Southern California Using Earthquake Seismograms and Ambient-Noise Correlagrams
En-Jui Lee, Po Chen, Thomas H. Jordan, Philip J. Maechling, Marine Denolle, and Gregory C. Beroza 1 SCEC, USC ; 2 University of Wyoming ; 3 Sripps , UCSD ; 4Stanford University
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0 2 4 6 8 10 12 14 16 18 20 22 24 26
x 105
Iteration Number
EBP
EFP
ABP
AFG
AFP
SI AW SI
↓ add ANGF
↓ CMT
↓ CMT
↓ CMT
↓ CMT
E#=100
E#=135
E#=160
Bar
s: N
umbe
r of
Mea
sure
men
ts
Cur
ve: R
WM
Red
uctio
n (%
)
0
0.6
1.2
1.8
2.4
3
3.6
4.2
4.8
5.4
6
10
20
30
40
50
60
70
80
90
100
−120˚ −118˚ −116˚ −114˚
32˚
33˚
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38˚Earthquake
4,671 windows
−120˚ −118˚ −116˚ −114˚
32˚
33˚
34˚
35˚
36˚
37˚
38˚ANGF (high&low)
3,176 windows
−120˚ −119˚ −118˚ −117˚ −116˚
34˚
35˚
36˚
(a)Isostatic Gravity Anomaly
1
2
3
4
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8
−70−60−50−40−30−20−10
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10
20
30mgal
−120˚ −119˚ −118˚ −117˚ −116˚
34˚
35˚
36˚
(b) Z2.5 of CVM−S4
SN
FZ
WWFGF
SAF
SAF
SJF
ECSZ
APF
1
2
3
4
5
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7
8
−120˚ −119˚ −118˚ −117˚ −116˚
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(c) Z2.5 of CVM−S4.26
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3
5
1
4
7
8
60
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8
Depth (km)
−120˚ −119˚ −118˚ −117˚ −116˚
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36˚
(d) Z2.5 of CVM−H11.9
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3
4
7
8
1
5
6
Abstract We have constructed a high-resolution model for the Southern California crust, CVM-S4.26, by inverting more than half-a-million waveform-mis�t measurements from about 38,000 earthquake seismograms and 12,000 ambient-noise correlagrams. The inversion was initiated with the Southern California Earthquake Center’s Community Velocity Model, CVM-S4, and seismograms were simulated using K. Olsen’s staggered-grid �nite-di�erence code, AWP-ODC, which was highly optimized for massively parallel computation on super-computers by Y. Cui et al. We navigated the tomography through 26 iterations, alternating the inversion sequences between the adjoint-wave�eld (AW) method and the more rapidly converging, but more data-intensive, scattering-integral (SI) method. Earthquake source errors were reduced at various stages of the tomographic navigation by inverting the wave-form data for the earthquake centroid-moment tensors. All inversions were done on the Mira supercomputer of the Argonne Leadership Computing Facility. The resulting model, CVM-S4.26, is consistent with independent observations, such as high-resolution 2D refraction surveys and Bouguer gravity data. Many of the high-contrast features of CVM-S4.26 conform to known fault structures and other geological constraints not applied in the inversions. We have conducted several other validation experiments, including checking the model against a large number (>28,000) of seismograms not used in the inversions. We illustrate this consis-tency with the excellent �ts at low frequencies (≤ 0.2 Hz) to three-component seismograms recorded throughout Southern California from the 17 Mar 2014 Encino (MW4.4) and 29 Mar 2014 La Habra (MW5.1) earthquakes, and we show these �ts to be much better than those ob-tained by two community velocity models in current use, CVM-S4 and CVM-H11.9. We con-clude by describing some of the novel features of the CVM-S4.26 model, which include un-usual velocity reversals in some regions of the mid-crust.
Figure 1. (a) Red solid line with circles: the relative waveform mis�t (RWM) for a set of waveforms selected for monitoring the improvements of our model. Vertical bars: the number of mis�t measurements used in each iteration. Colors of the vertical bars indicate the di�erent types of the mis�t measurements used. Vertical dash lines separate iterations carried out using the AW method from those carried out using the SI method. Black arrows indicate the iterations in which CMT inversions were performed or ambient-noise correlagrams were included. The number of earthquakes used in each iteration is shown following “E#=.” (b) Source-receiver paths for the 4671 earthquake waveforms used for monitoring the RWM reduction. Black stars: earthquake epicenters; red triangles: broadband stations. (c) Interstation paths for the 3176 Rayleigh waves on the ambient-noise correlagrams (Appendix A) used for monitoring the RWM reduction. Black triangle: stations used as virtual sources; red triangles: stations used as receivers. The source-receiver paths for these selected waveforms are shown as green lines in Figures 1b and 1c.
Figure 2. Maps of (a) isostatic gravity anomaly and (b~d) Z2.5 maps for CVMs in Southern California. The basin structures not well represented in the initial model, CVM-S4, are numbered: (1) Santa Maria Basin, (2) Southern San Joaquin Basin (SSJB), (3) Owens Valley (OV), (4) Indian Wells Valley (IWV), (5) Santa Barbara Channel (SBC), (6) Santa Monica Basin, (7) Antelope Valley (AV), and (8) San Bernardino Basin (SBB). Some faults are marked on (b): San Andreas Fault (SAF), White Wolf Fault (WWF), Sierra Nevada Fault Zone (SNFZ), Arroyo Parida Fault (APF), Garlock Fault (GF), Eastern California Shear Zone (ECSZ), and San Jacinto Fault (SJF).
Figure 3. (a) S wave velocities at (top) 2 km, (middle) 10 km, and (bottom) 20 kmdepths in (left) CVM-S4, (middle) CVM-S4.26, and (right) CVM-H11.9. The color bar on the upper left corner of each plot shows the range of the color scale with red indicating relatively slow S wave velocities and blue indicating relatively fast S wave velocities. Green dash line boxes on left column indicate the tomography region of Tape et al. [2009, 2010]. Black solid lines show major faults in Southern California. Numbers shown in the top row, middle column indicate locations of some geological features. 1: Southern San Joaquin Basin (SSJB); 2: Santa Maria Basin; 3: Salinian basement outcrop; 4: Cuyama Basin; 5: Ring-dike complexes; 6: Long-Valley Caldera; 7: Big Pine Volcanic Field; 8: Owens Lake; 9: IndianWell’s Valley (China Lake); 10: Searles Lake; 11: Santa Barbara Channel; 12: Antelope Valley; 13: Santa Monica Basin; 14: Catalina Schist outcrop; 15: San Bernardino Basin; 16: Peninsular Ranges Batholith.
−20
−10
0
WWF GF ʼAA
CVM−S4.26
−20
−10
0
WWF GF ʼAA
CVM−S4
−20
−10
0
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WWF GF ʼAA
CVM−H11.9
LF GH−HF ʼBB
CVM−S4.26
LF GH−HF ʼBB
CVM−S4
0 20 40 60
LF GH−HF ʼBB
CVM−H11.9
3.5
SSF SGF SAF ʼCC
CVM−S4.26
SSF SGF SAF ʼCC
CVM−S4
0 20 40 60 80
3.5
SSF SGF SAF ʼCC
CVM−H11.9
4
WF SMFZ SAFSGF ʼDD
CVM−S4.26
WF SMFZ SAFSGF ʼDD
CVM−S4
0 20 40 60
WF SMFZ SAFSGF ʼDD
CVM−H11.9
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ʼEE
CVM−S4.26
ʼEE
CVM−S4
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ʼEE
CVM−H11.9
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−10
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3.5
BF SAF JVF ʼFF
CVM−S4.26
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BF SAF JVF ʼFF
CVM−S4
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BF SAF JVF ʼFF
CVM−H11.9
2.25
2.50
2.75
3.00
3.25
3.50
3.75
4.00
4.25Vs (km/s)
−120˚ −118˚ −116˚
34˚
36˚
15481673
SOL
ADO
BOR
BTP
CIA
CLC
EDW2
IRMLAF
MCTMOP
SDD
SMR
SPG2
TUQ
RXH
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SDD−Z
SDD−R
SDD−T
CVM−S4
0 25 50
CVM−S4.26
0 25 50
CVM−H11.9
25 50
ADO−Z
ADO−R
ADO−T
25 50 25 50
30 60 90 120
CLC−Z
CLC−R
CLC−T
CVM−S4
30 60 90 120
CVM−S4.26
30 60 90 120
CVM−H11.9
60 90 120
RXH−Z
RXH−R
RXH−T
60 90 120 60 90 120
60 90 120
SPG2−Z
SPG2−R
SPG2−T
60 90 120 60 90 120
60 90 120
IRM−Z
IRM−R
IRM−T
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60 90 120
TUQ−Z
TUQ−R
TUQ−T
60 90 120 60 90 120
60 90 120 150
SMR−Z
SMR−R
SMR−T
60 90 120 150time (sec)
60 90 120 150
30 60
LAF−Z
LAF−R
LAF−T
CVM−S4
30 60
CVM−S4.26
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CVM−H11.9
30 60
BTP−Z
BTP−R
BTP−T
30 60 30 60
30 60
EDW2−Z
EDW2−R
EDW2−T
30 60 30 60
30 60
SOL−Z
SOL−R
SOL−T
30 60time (sec)
30 60
30 60
CIA−Z
CIA−R
CIA−T
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30 60 90
MOP−Z
MOP−R
MOP−T
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30 60 90
BOR−Z
BOR−R
BOR−T
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30 60 90
MCT−Z
MCT−R
MCT−T
30 60 90time (sec)
30 60 90
Community Velocity Models (CVM-S4, CVM-S4.26, & CVM-H11.9)
Iterative Inversions
Basin Structures
Figure 4. Cross sections of CVMs, including the CVM-S4, CVM-S4.26, and CVM-H11.9. On the velocity pro�les, the black lines represent projected fault surfaces from the SCEC Community Fault model (CFM) (14); the purple lines are from the Carena & Suppe’s fault model; brown lines are interpreted de-collement from LARSE surveys. The velocity contrasts on the cross-sections of CVM-S4.26 show high consistencies with the 3D fault models. The num-bers on the map indicate the (1) GF, (2) SNFZ, (3) SAF, (4) Elsinore Fault, and (5) SJF. Faults labeled on cross-sections for reference are Lenwood Fault (LF), Gravel Hills-Haper Fault (GH-HF), Santa Susana Fault (SSF), San Gabriel Fault (SGF), Whittier Fault (WF), Sierra Madre Fault Zone (SMFZ), Banning Fault (BF), and Johnson Valley Fault (JVF).
Fault Structures
Waveform Comparisons of La Habra Event (Not Used in the Inversion)Figure 5. Examples of observed (black) and synthetic (red) seismograms for the La Habra earthquake. For each station, observed and synthetic seismograms of the vertical, radial and transverse components are shown from top to bottom and synthetics computed using CVM-S4, CVM-S4.26 and CVM-H11.9 are shown from left to right. The beachball shows the CMT solu-tion used for computing the synthetics. Yellow star: epicenter location; white triangles: 3-component broadband stations whose seismograms are shown.
References & Acknowledgements
Lee, E., Chen, P., and Jordan, T. H. (2014). Testing Wave-form Predictions of 3D Velocity Models Against Two Recent Los Angeles Earthquakes, Seismological Re-search Letters, (in press) Lee, E., Chen, P., Jordan, T. H., Maechling, P. B., Denolle, M. A. M., and Beroza, G. C. (2014). Full-3D Tomography (F3DT) for Crustal Structure in Southern California Based on the Scattering-Integral (SI) and the Adjoint-Wave�eld (AW) Methods, Journal of Geophysical Re-search, (in press). Tape, C., Liu, Q., Maggi, A., Tromp, J., (2009). Adjoint tomography of the southern California crust. Science 325, 988–992. Support for this work was provided by Southern Cali-fornia Earthquake Center (SCEC).
CVM−S4 Vs @ 2 km
−120˚ −118˚ −116˚ −114˚
33˚
34˚
35˚
36˚
37˚
38˚
A
A’
D
D’
C
C’
F
F’
E
E’
B
B’
2.42.62.83.03.23.43.6
CVM−S4.26 Vs @ 2 km
−120˚ −118˚ −116˚ −114˚
1
2
3
4
6
7
8
910
11
12
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14
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5
16
2.42.62.83.03.23.43.6
CVM−H11.9 Vs @ 2 km
−120˚ −118˚ −116˚ −114˚
33˚
34˚
35˚
36˚
37˚
38˚
2.42.62.83.03.23.43.6
CVM−S4 Vs @ 10 km
−120˚ −118˚ −116˚ −114˚
33˚
34˚
35˚
36˚
37˚
38˚
3.03.23.43.63.84.04.2
CVM−S4.26 Vs @ 10 km
−120˚ −118˚ −116˚ −114˚
3.03.23.43.63.84.04.2
CVM−H11.9 Vs @ 10 km
−120˚ −118˚ −116˚ −114˚
33˚
34˚
35˚
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37˚
38˚
34˚
36˚
38˚
3.03.23.43.63.84.04.2
CVM−S4 Vs @ 20 km
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37˚
38˚
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3.6
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4.0
4.2
CVM−S4.26 Vs @ 20 km
−120˚ −118˚ −116˚ −114˚
3.4
3.6
3.8
4.0
4.2
CVM−H11.9 Vs @ 20 km
−120˚ −118˚ −116˚ −114˚
33˚
34˚
35˚
36˚
37˚
38˚
3.4
3.6
3.8
4.0
4.2
(b) (c)
(a)