A high resolution seismic reflection profile at the Prince Ranch, South Dakota

Attenuation estimates quantify the loss of energy of propagating seismic waves due to anelastic processes. It is often carried out in the frequency domain. The most well-known methods for attenuation estimation, such as the spectral ratio and frequency-shift methods, compare spectral shapes of waveforms along a given raypath. They require broad spectra such as those obtained with the Fourier transform and the continuous wavelet transform. These methods are incompatible with high-resolution time-frequency transforms, which drastically localize time-frequency information. On the other hand, these transforms indicate stronger resistance to noise and can be used in combination with the peak frequency method to estimate attenuation. We have applied high-resolution transforms, namely the synchrosqueezing transform, basis pursuit, and complete ensemble empirical-mode decomposition, to a synthetic wedge example and two seismic data set examples, a seismic reflection profile, and a vertical seismic profile (VSP). Results for the synthetic example find that most high-resolution transforms are able to reliably estimate quality factors. Using centroid frequencies, the seismic reflection profile exhibits local increases in centroid frequencies, which likely indicates imprints from apparent attenuation over intrinsic attenuation. Centroid frequencies and effective quality factors for the VSP are consistent for the different spectral estimation techniques. These three examples illustrate the value of high-resolution transforms for frequency and quality factor measurements.

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Seismic Hazard of L'Aquila downtown (central Italy): new insights for 3D geological model based on high-resolution seismic reflection profile and borehole stratigraphy

10.5194/se-2019-25 ◽

2019 ◽

Author(s):

Marco Tallini ◽

Marco Spadi ◽

Domenico Cosentino ◽

Marco Nocentini ◽

Luca Macerola ◽

...

Keyword(s):

High Resolution ◽

Seismic Hazard ◽

Seismic Reflection ◽

Site Effects ◽

Central Italy ◽

Seismic Reflection Profile ◽

Geological Model ◽

Reflection Profile ◽

3D Geological Model ◽

Geophysical Surveys

Abstract. On 6 April 2009, a Mw 6.1 earthquake struck the Plio-Quaternary intermontane L'Aquila Basin in central Italy, causing strong damages in L'Aquila historical downtown and surroundings, which were affected by notable site effects. Previous works have suggested that different site effects may be related to the complex subsurface geologic architecture, given by the variability of thickness and lithology of L'Aquila Basin clastic deposits, on which the city was built. To improve the 3D geological model of L'Aquila downtown for seismic site response evaluation and to estimate the Seismic Hazard of possible buried active normal faults, a multitask project has been carried out consisting mainly of the integration of subsurface dataset, including geological and geophysical surveys. Data have been interpreted with the aim to conceive and build a detailed model for the Plio-Quaternary cover of the continental basin and the buried morphology of the Meso-Cenozoic bedrock. We report the results concerning the interpretation of a 1 km-long high-resolution seismic reflection profile and refraction tomography integrated with the stratigraphy from deep and shallow boreholes. The results allowed us to reconstruct the Plio-Quaternary succession below L'Aquila downtown. The Plio-Quaternary depocentre corresponds to a minor NNW-SSE graben, which is developed within the main regional graben that borders L'Aquila Basin. Finally, data interpretation allowed to reconstruct the Plio-Quaternary tectono-stratigraphic evolution of the basin, to evidence the recent activity of several faults, and to define the subsoil geological model of the study area. All these data, which are functional to define the seismic site effects and to detect the activity of faults, are useful to mitigate the Seismic Hazard of cultural heritage cities of central Italy, such as the case study of L'Aquila downtown.

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