A deterministic approach toward isostatic gravity residuals: A case study from South America

Chapin, David A.

doi:10.1190/1.1932114

Cited by 10 publications

(29 citation statements)

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“…The reference crustal thickness (i.e., crustal thickness at sea level) is taken as 35 km on the basis of information from refraction seismic investigations from the Brazilian Craton east of the Andes [Götze and Kirchner, 1997]. These values are similar to those used by other authors [Whitman, 1994;Chapin, 1996].…”

Section: Gravity Data Acquisition and Isostatic Residual Anomaly Procmentioning

confidence: 99%

Asperity generating upper crustal sources revealed by b value and isostatic residual anomaly grids in the area of Antofagasta, Chile

et al. 2007

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[1] In our study we show that the locations of largest coseismic slip (asperities) on the fault plane of the M w = 8.0 1995 Antofagasta earthquake in Northern Chile can be mapped by the spatial distribution of the seismic b value obtained from the aftershock sequence of the megathrust earthquake. These areas of high seismic moment release and concurrent high-b values are congruent with anomalies of the gravity isostatic residual (IR) field in the Antofagasta region. They are superimposed on the seismogenic part of the north Chilean subduction zone where the strongest coupling of the upper and lower plate is expected. The IR anomalies are interpreted to be caused by large Jurassic-Early Cretaceous batholiths which intruded into the upper crust. The observed positive correlations between high seismic b values, IR anomalies, and geologic structures enable us to propose a mechanical model for the generation of the asperities in the Antofagasta region. We suggest that the batholiths in conjunction with buoyant forces acting on the subducted slab of the Nazca plate are responsible for locking the interface where the asperities are located. This implies long-term conditions for the existence of the asperity generating tectonic situation. Concequently, the asperities around Antofagasta could be stationary features, at least for several seismic cycles. Hence we propose that the IR anomalies along the north Chilean convergent margin can be used as an indicator for high moment release and slip in future large earthquakes.

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Section: Gravity Data Acquisition and Isostatic Residual Anomaly Procmentioning

confidence: 99%

Asperity generating upper crustal sources revealed by b value and isostatic residual anomaly grids in the area of Antofagasta, Chile

et al. 2007

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“…Towards this points different methods have been developed by previous authors. Thorarinsson & Magnusson (1990) first and then Chapin (1996) introduced the interesting concept of scaling analysis to reduce the short-wavelength correlation between topography and Bouguer anomaly for a given data set. Their results seemed to be quite discordant concerning the optimization procedure, but we are going to show that probably they are more in agreement than they seem.…”

Section: E T E R M I N I N G T H E O P T I M a L B O U G U E R D E mentioning

confidence: 99%

“…When there is a large data set as in our case, self-affinity is more rapidly evaluated by the slope of the radial power spectrum by a double logarithmic scale. The work of Chapin (1996) was developed in this sense, by performing a simple Bouguer correction by the slab factor, neglecting terrain corrections, and then by analysing the fractal dimension given by the radial power spectrum in the Fourier domain. His optimization was based on minimization of the difference between a linear decay of the fractal dimension with density and the observed trend.…”

Section: The Scaling Approachmentioning

confidence: 99%

“…He realized however that his result did not exhibit a minimum for the curve fractal dimension versus density, being thus not compatible with the work of Thorarinsson & Magnusson (1990), that showed instead a U-shaped trend. Chapin (1996) proposed a possible explanation as due to the limited areal extent of Thorarinsson & Magnusson (1990) data to measure accurately the fractal dimension. We think instead that this difference should derive also from the terrain contribution, where the topographic effect play a major role in affecting the short-wavelength gravity field by a scaling contamination.…”

Section: The Scaling Approachmentioning

confidence: 99%

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Determining the optimal Bouguer density for a gravity data set: implications for the isostatic setting of the Mediterranean Sea

Tontini¹,

Graziano²,

Cocchi

et al. 2007

Geophysical Journal International

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S U M M A R YWe have used free-air gravity satellite data from GEOSAT and ERS-1 missions to compile a Bouguer gravity map of the Mediterranean Sea. The complete Bouguer correction has been applied by using the method of Parker, that acts in the Fourier domain and permits the exact evaluation of the gravity contribution from an highly sampled topographic model of the land. The density used for the Bouguer reduction has been obtained from the gravity data set itself, by using two different optimization methods that have given the same optimal result of 2400 kg m −3 . We have studied the radial power spectrum of the data, choosing the optimal Bouguer density from its slope, as the one which minimizes the fractal dimension of the resulting gravity map. The second approach consists of studying the correlation between topography and Bouguer anomaly by spatial cross-plots for a significant subset of the data. Both these approaches are aimed at reducing the short-wavelength effects of topography in the gravity map, but in the past they have been traditionally used alternatively since they gave different optimization values, especially the second method that seems to ignore large-wavelength isostatic effects. Actually, we have revisited both the methodologies, proposing slight modifications to make their efforts compatible. Their coincident results confirm their validity of application and give reliability to the recovered value of the Bouguer optimal density. Moreover, modifying the second approach allows us to compile a sort of normalized correlation map, which we propose in this paper, defining the 2-D isostatic setting of the investigated region without introducing any further lithospheric model. The final result is a revised Bouguer map compiled using a grid with a resolution of 2 min, that is useful for large-scale geological studies and gives important information about the compensation mechanism of the Mediterranean Sea: in a direct way we have found that the overall region seems to be in a complete isostatic equilibrium apart from the young basins of Tyrrhenian Sea and Aegean Sea, confirming previous similar results.

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“…It is interesting to note that at short wavelengths free‐air and Bouguer gravity follow the same scaling law, reflected in equal scaling exponents. The self‐similarity of the gravity field is probably due to a self‐similar density distribution in the crust Pilkington & Todoeschuck 1990; Maus & Dimri 1996) combined with self‐similar topographic anomalies (Chapin 1996). Above wavelengths of around 50 km the slope of the power spectrum decreases, indicating a reduced power for long‐wavelength gravity anomalies.…”

Section: Expected Power Spectrum Of the True Geoidmentioning

confidence: 99%

Improved ocean-geoid resolution from retracked ERS-1 satellite altimeter waveforms

1998

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The ocean geoid can be inferred from the topography of the mean sea surface. Satellite altimeters transmit radar pulses and determine the return traveltime to measure seasurface height. The ERS-1 altimeter stacks 51 consecutive radar reflections on board the satellite to a single waveform. Tracking the time shift of the waveform gives an estimate of the distance to the sea surface. We retrack the ERS-1 radar traveltimes using a model that is focused on the leading edge of the waveforms. While earlier methods regarded adjacent waveforms as independent statistical events, we invert a whole sequence of waveforms simultaneously for a spline geoid solution. Smoothness is controlled by spectral constraints on the spline coefficients. Our geoid solutions have an average spectral density equal to the expected power spectrum of the true geoid. The coherence of repeat track solutions indicates a spatial resolution of 31 km, as compared to 41 km resolution for the ERS-1 Ocean Product. While the resolution of the latter deteriorates to 47 km for wave heights above 2 m, our geoid solution maintains its resolution of 31 km for rough sea. Retracking altimeter waveform data and constraining the solution by a spectral model leads to a realistic geoid solution with significantly improved along-track resolution.

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A deterministic approach toward isostatic gravity residuals: A case study from South America

Cited by 10 publications

References 0 publications

Asperity generating upper crustal sources revealed by b value and isostatic residual anomaly grids in the area of Antofagasta, Chile

Asperity generating upper crustal sources revealed by b value and isostatic residual anomaly grids in the area of Antofagasta, Chile

Determining the optimal Bouguer density for a gravity data set: implications for the isostatic setting of the Mediterranean Sea

Improved ocean-geoid resolution from retracked ERS-1 satellite altimeter waveforms

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