3,560 research outputs found
Validating tomographic model with broad-band waveform modelling: an example from the LA RISTRA transect in the southwestern United States
Traveltime tomographic models of the LA RISTRA transect produce excellent waveform fits if we amplify the damped images. We observe systematic waveform distortions across the western edge of the Great Plains from South American events, starting about 300 km east of the centre of the Rio Grande Rift. The amplitude decreases by more than 50 per cent within array stations spanning less than 200 km while the pulse width increases by more than a factor of 2. This feature is not observed for the data arriving from the northwest. While the S-wave tomographic image shows a fast slab-like feature dipping to the southeast beneath the western edge of the Great Plains, synthetics generated from this model do not reproduce the waveform characteristics. However, once we modify the tomographic image by amplifying the velocity contrast between the slab and adjoining mantle by a factor of 2–3, the synthetics produce observed amplitude decay and pulse broadening. In addition to the traveltime delay, amplitude variation due to wave phenomena such as slab diffraction, focusing and defocusing provide much tighter constraints on the geometry of the fast anomaly and its amplitude and sharpness as demonstrated by a forward sensitivity test and snapshots of the seismic wavefield. Our preferred model locates the slab 200 km east of the Rio Grande Rift dipping 70°–75° to the southeast, extending to a depth near 600 km with a thickness of 120 km and a velocity of about 4 per cent fast. In short, adding waveform and amplitude components to regional tomographic studies can help validate and establish structural geometry, sharpness and velocity contrast
Harmonic map flow with low -energy
Let be a compact oriented surface and a compact K\"ahler
manifold with nonnegative holomorphic bisectional curvature. For harmonic map
flow starting from a map with low -energy, the
limit at each singular time extends continuously over the bubble points and no
necks appear.Comment: 31 pages, 1 figur
Large Trench-Parallel Gravity Variations Predict Seismogenic Behavior in Subduction Zones
We demonstrate that great earthquakes occur predominantly in regions with
a strongly negative trench-parallel gravity anomaly (TPGA), whereas regions
with strongly positive TPGA are relatively aseismic. These observations suggest
that, over time scales up to at least 1 million years, spatial variations of
seismogenic behavior within a given subduction zone are stationary and linked
to the geological structure of the fore-arc. The correlations we observe are
consistent with a model in which spatial variations in frictional properties on
the plate interface control trench-parellel variations in fore-arc topography,
gravity, and seismogenic behavior
Slip distribution and tectonic implication of the 1999 Chi‐Chi, Taiwan, Earthquake
We report on the fault complexity of the large (M_w = 7.6) Chi‐Chi earthquake obtained by inverting densely and well‐distributed static measurements consisting of 119 GPS and 23 doubly integrated strong motion records. We show that the slip of the Chi-Chi earthquake was concentrated on the surface of a ”wedge shaped” block. The inferred geometric complexity explains the difference between the strike of the fault plane determined by long period seismic data and surface break observations. When combined with other geophysical and geological observations, the result provides a unique snapshot of tectonic deformation taking place in the form of very large (>10m) displacements of a massive wedge‐shaped crustal block which may relate to the changeover from over‐thrusting to subducting motion between the Philippine Sea and the Eurasian plates
Multi-spatial-mode effects in squeezed-light-enhanced interferometric gravitational wave detectors
Proposed near-future upgrades of the current advanced interferometric
gravitational wave detectors include the usage of frequency dependent squeezed
light to reduce the current sensitivity-limiting quantum noise. We quantify and
describe the degradation effects that spatial mode-mismatches between optical
resonators have on the squeezed field. These mode-mismatches can to first order
be described by scattering of light into second-order Gaussian modes. As a
demonstration of principle, we also show that squeezing the second-order
Hermite-Gaussian modes and , in addition
to the fundamental mode, has the potential to increase the robustness to
spatial mode-mismatches. This scheme, however, requires independently optimized
squeeze angles for each squeezed spatial mode, which would be challenging to
realise in practise.Comment: 10 pages, 12 figure
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