Such a correlation provides a strong indication that lateral variations in the occurrence of large earthquakes in a given subduction zone are strongly associated with the forearc structure and topographic features such as basins and peninsulas. In Chapter 2, I present modeling of very long free Earth oscillations of the giant Sumatra-Andaman earthquake.
Introduction
The number in the upper left corner of each cell indicates the percentage of total torque associated with the corresponding area of TPGA and TPTA. Results from viscous models (4, 5), visco-elastic models (6, 7), and laboratory experiments (8) suggest that spatial variations in the magnitude of shear features at the plate interface can modulate surface topography and gravity in the fore-arc.
Supplementary Materials and Methods
- Construction of TPGA
- Estimation of TPGA associated with subduction zone earthquakes
- Construction of TPTA
- Moment release versus TPGA
- Robustness of correlation between TPGA and seismic moment
The removal of the mean trench normal profile serves to place all subduction zones on a more comparable basis. The total cumulative seismic moment is dominated by the three largest earthquakes of the 20th century.
National Geophysical Data Center, Total Sediment Thickness of the World's Oceans & Marginal Seas, Natl. S18.National Geophysical Data Center, Total Sediment Thickness of the World’s Oceans & Marginal Seas, Natl.
Introduction
Broadband seismography data
Free oscillation spectra for GSN station QSPA, whose sensor is located in an ice borehole in the silent sector of the South Pole station. The relative excitation of the m = ±1 vibration modes of 0S2 is significantly underpredicted by this location centroid.
Earthquake size and duration
The initial phase of a free oscillation of period, T, is aligned with the time centroid of the rupture process if the rupture duration is relatively small, i.e. τ T. Many factors indicate that fault movement was greater and faster in the south of the fault zone, where rupture began, and was smaller and slower in the north.
Modeling the rupture
S p e c t r u m comparison for the 26 December 2004 Sumatra-Andaman and 28 March 2005 North Sumatra earthquakes with 127-hour records of vertical motion recorded at station KMBO (Kilima Mbogo, Kenya). Spectral predictions of the Harvard CMT solutions are presented in graph form as well as spectra predicted from finite fraction. Note the greater success of the CMT solution for the 2005 event, consistent with a less complex fracture process.
Supplementary material
For the 2004 Sumatra-Andaman earthquake, modes 0S2, 0S3, 0S4, and 1S2 were observed with an unprecedented signal-to-noise ratio. The misfit is defined as the normalized difference between absolute values of the Hann tapered discrete Fourier transform. For 9 Geoscope stations we plot the amplitude increase relative to the Harvard CMT solution, against the initial phase of the oscillation at the onset of the rupture.
The 410 km (410) seismic discontinuity in the mantle is generally attributed to a phase transition from olivine to the wadsleyite structure (M g, F e)2SiO4, while the 660 (660) seismic discontinuity is likely due to a phase transition from (M g, F e) 2SiO4 ringwoodite to perovskite and magnesiustite1,2. We simultaneously model seismic refracted waves and scattered waves from 410 to constrain fine structures near 410. We find a low-velocity zone (LVZ, 5% shear wave velocity drop) on top of 410 beneath the northwestern United States, extending from southwestern Oregon to northern basin and mountain range.
Introduction
Data and Modeling
The observed branches AB and CD of recording section A (circle) and recording section B (square) are plotted with red and blue symbols, respectively (see also Fig. 1 for ray paths). Record section F (recorded by XM PASSCAL stations, see Fig. 3.1) and synthetics from a hybrid LVZB model (70 km LVZ + 60 km topographic depression) are shown in the two right columns. Record section C (Fig. 3.5) samples the northern Basin and Range province and shows an anomalous secondary pulse appearing at epicentral distances of 22-23 degrees, which is also seen in recorded sections D and F (Fig.
Discussion
The arrow points to the negatively converted pulse due to the existence of the LVZ on top of the 410. Under such circumstances, we can produce the complicated converted pulse from the 410 and the negative pulse from the LVZ on top of the 410 (Fig. 3.7, see section) 3.4). We could not reproduce receiver functions with a strong negative pulse without inserting an LVZ on top of the 410.
Supplementary information
The geographic coincidence between the unique HAOT and LVZ at Peak 410 in the Northwest Basin and Range may suggest that they are likely related to tectonic processes such as Farallon plate subduction and surface extension in the back-arc regime17. If the water content is high enough in the transition zone, the LVZ can form directly above 410 in the uplifted material as a result of dehydration melting25. These synthetic receiver functions are calculated from velocity models with variations in the thickness (20–90 km) of the LVZ at the top of 410 and discontinuous topography (20–60 km).
Isotope and trace element constraints on the composition and evolution of the lithosphere beneath the southwestern United States. Using converted phases to infer the depth of the lithosphere-asthenosphere boundary beneath South America, J. Although the geometry of the LVZ is not unique due to the limited data analyzed, the sharp edge of the LVZ is strongly constrained by the available array data.
Introduction
The intersection of branches AB and CD is used to determine the depth and size of the discontinuity. The movement and amplitude of the CD branches forward beyond the intersection of AB and CD shows its velocity and gradient below the seismic discontinuity 410. With the help of the time between the AB and CD branches, we can determine the reduction of the velocity of the LVZ and its thickness even though it has exchanges.
Data and Waveform Analysis
Waveform modeling with 1D layered models
Perturbated velocity models near the breakpoint of the CD branch are generated as a sensitivity study. The size of the disturbances is estimated as the size of the Fresnel zone in the direction of the longitudinal and transverse paths. After branch AB and CD intersect, the gradient model often predicts an earlier appearance of branch AB near 21.5◦ .
Modeling complex structures
In general, data recorded on the eastern side of the Californa shear zone can be explained with a low-velocity zone boundary north of Lake Tahoe. Data best fitted by the 3D LVZ model where the edge of LVZ on the east/west side of the station is beyond the illuminated zone is plotted in dark blue/dark red. Data best fitted by the 3-D LVZ model where the edge of LVZ on the east/west side of the station is within the illuminated zone is plotted in light blue/light red.
Discussion
These trails primarily sample the regions below southern Oregon, northern California, and the western edge of the Basin and Range. Above 1473 K, that is, at normal mantle temperature in the transition zone, dehydration of wadsleyite with water can produce a hydrous plume and affect the chemical differentiation of the upper mantle. As suggested by ?, a stagnant slab in the transition zone is a good reservoir to store dense hydrous magnesium silicate, the E phase, at less than 1473 K.
Conclusion
Appendix
Finite difference
Diffracted Finite difference (DiFD)
If the field along the line Γ is uniform (independent of the azimuth), this line integration yields a. However, if the left side is delayed relative to the right side, we obtain a split response, as discussed in. Thus, to account for variations in velocities in the third dimension, a 2D Kirchhoff line integral is performed to sum all secondary sources. on a reference plane S along the line Γ (Fig. 4.15).
Estimate zone of influence
The bottom diagram (c) shows the time corresponding to the above four positions according to the square root weighting. Tomographic traveltime models of the La Ristra transect produce excellent waveform fits when the blurred images are amplified into different structures. While the tomographic image shows a fast slab-like feature dipping to the southeast beneath the western edge of the Great Plains, the synthetics generated from this model do not reproduce the waveform observations.
Introduction
The range (red stars) intersects the Great Plains, the Rio Grande Rift, and the Colorado Plateau. However, station NM15 is located near the transition region between the slow rift zone and the fast plate. We will further analyze P-waveforms in a separate chapter and the collective results will provide important constraints on the physical state and composition of this interesting slab feature beneath the western margin of the cratonic Great Plains near the Rio Grande Rift.
Waveform Data
The observed waveform distortion and amplitude variations are consistent regardless of the location and depth of various events at the SE suggesting receiver-side structure effects (Fig. 5.7). All four record sections show systematic amplitude decrease and waveform broadening at stations NM07- NM18. All the deconvolved record sections from four events to the SE show consistent results where the peak amplitude of the S-wave from station NM07 to NM18 decreases by a factor of 2-3 and the pulse widths broaden by a factor of 2-3, independently of the source depth and epicentral distance (Fig. 5.9).
Finite Difference Modeling
Regional tomography model: ?, ?
We generate synthetic waveforms and present traveltime delays and amplitude ratios relative to reference station NM07. 5.11, the preferred model A also has the smallest mismatch in traveltime delays and amplitude decay (see Table 5.2). The lower left panel shows the comparison of measured travel time delays and predictions.
Idealized Model Sensitivity: Slab Thickness and Geometry
The first row presents comparisons of synthetic amplitude ratios versus plate velocity anomaly (model I.A, I.B, I.C). The second row presents comparisons of synthetic amplitude ratios versus slab depth (model I.A, I.D, I.E). In addition, the amplitude variation across the plate also provides information on the depth extent of the plate.
Discussion and Conclusion
By using both travel time and amplitudes, we can mostly eliminate trade-offs between the geometry of the plate and its velocity variance. The sheet feature is also displaced eastward from the center of the Rio Grande Rift Zone by 200 km. We have presented a systematic analysis of the use of amplitude information in the exploration of the plate-like structure beneath the eastern margin of the Rio Grande rift in the southwestern United States.
Introduction
In this study, we will model the P waveforms following the same procedure used in the S wave study. We then estimate the contrast in M g#, temperature, and density in the deep upper mantle across the western Great Plains and Rio Grande Rift. Finally, we discuss its implications for the origin of the plate-like feature near the edge of the stable continental Great Plains and Rio Grande Rift in the southwestern United States.
Observations
To model these records, we simply scaled the S-wave model obtained by modeling sections of the S-wave record to a P-wave model using different SFs ranging from 1 to 2. We found that the P waveforms fit best well in shape, time delay and amplitude ratio with an SF close to 1.25. The geometry of the problem provides a way to directly compare the continental lithosphere with the mantle asthenosphere.
