TY  - JOUR
A1  - Ramos, Catalina
A1  - Mechie, James
A1  - Stiller, Manfred
T1  - Reflection seismic images and amplitude ratio modelling of the Chilean subduction zone at 38.25 degrees S
JF  - Tectonophysics : international journal of geotectonics and the geology and physics of the interior of the earth
N2  - Active source near-vertical reflection (NVR) data from the interdisciplinary project TIPTEQ were used to image and identify structural and petrophysical properties within the Chilean subduction zone at 38.25 degrees S, where in 1960 the largest earthquake ever recorded (M-w 9.5) occurred. Reflection seismic images of the subduction zone were obtained using the post-stack depth migration technique to process the three components of the NVR data, allowing to present P- and S-stacked time sections and depth-migrated seismic reflection images. Next, the reflectivity method allowed to model traveltimes and amplitude ratios of pairs of reflections for two 1D profiles along the studied transect. The 1D seismic velocities that produced the synthetic seismograms with amplitudes and traveltimes that fit the observed ones were used to infer the rock composition of the different layers in each 1D profile. Finally, an image of the subduction zone is given. The Chilean subduction zone at 38.25 degrees S underlies a continental crust with highly reflective horizontal, as well as dipping events. Among them, the Lanalhue Fault Zone (LFZ), interpreted to be east-dipping, is imaged to very shallow depths for the first time. In terms of seismic velocities, the inferred composition of the continental crust is in agreement with field geology observations at the surface along the profile. Furthermore, no measurable amounts of fluids above the plate interface in the continental crust in this part of the Chilean subduction zone are necessary to explain the results. A large-scale anisotropy in the continental crust and upper mantle is qualitatively proposed. However, quantitative studies on this topic in the continental crust of the Chilean subduction zone at 38.25 degrees S do not exist to date.
KW  - Reflection seismics
KW  - Reflectivity method
KW  - Subduction zone
KW  - South America
Y1  - 2018
U6  - https://doi.org/10.1016/j.tecto.2018.10.007
SN  - 0040-1951
SN  - 1879-3266
VL  - 747
SP  - 115
EP  - 127
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Ramos, C.
A1  - Mechie, James
A1  - Feng, M.
T1  - Shear wave velocity and Poisson's ratio models across the southern Chile convergent margin at 38°15′S
JF  - Geophysical journal international
N2  - Using active and passive seismology data we derive a shear (S) wave velocity model and a Poisson's ratio (σ) model across the Chilean convergent margin along a profile at 38°15′S, where the Mw 9.5 Valdivia earthquake occurred in 1960. The derived S-wave velocity model was constructed using three independently obtained velocity models that were merged together. In the upper part of the profile (0–2 km depth), controlled source data from explosions were used to obtain an S-wave traveltime tomogram. For the middle part (2–20 km depth), data from a temporary seismology array were used to carry out a dispersion analysis. The resulting dispersion curves were used to obtain a 3-D S-wave velocity model. In the lower part (20–75 km depth, depending on the longitude), an already existent local earthquake tomographic image was merged with the other two sections. This final S-wave velocity model and already existent compressional (P) wave velocity models along the same transect allowed us to obtain a Poisson's ratio model. The results of this study show that the velocities and Poisson's ratios in the continental crust of this part of the Chilean convergent margin are in agreement with geological features inferred from other studies and can be explained in terms of normal rock types. There is no requirement to call on the existence of measurable amounts of present-day fluids, in terms of seismic velocities, above the plate interface in the continental crust of the Coastal Cordillera and the Central Valley in this part of the Chilean convergent margin. This is in agreement with a recent model of water being transported down and released from the subduction zone.
KW  - Controlled source seismology
KW  - Seismic tomography
KW  - Computational seismology
KW  - South America
Y1  - 2016
U6  - https://doi.org/10.1093/gji/ggv541
SN  - 0956-540X
SN  - 1365-246X
VL  - 204
SP  - 1620
EP  - 1635
PB  - Oxford Univ. Press
CY  - Oxford
ER  -