Velocity structure of the Vulsinian Volcanic Complex (Latium, Italy) from seismic refraction data and three-dimensional inversion of travel times

As part of a multidisciplinary investigation of the structure and tectonics of the Queen Charlotte Basin and underlying crust, deep multichannel seismic reflection and coincident crustal refraction data were collected in 1988. Energy from the reflection air-gun array source was recorded at land sites at offsets appropriate to record crustal refraction and wide-angle reflection data. Refraction data recorded in a broadside geometry provide good three-dimensional coverage of western Hecate Strait. These data are modelled using tomographic inversion techniques to determine the three-dimensional velocity structure of the crust in this region. The one-dimensional average velocity increases rapidly with depth to 6.5 km/s at 7 km depth. Velocities from 7 to at least 12 km depth remain approximately constant and are associated with rocks of the Wrangellia terrane. Significant lateral velocity variations, including large differences in near-surface velocities attributable to surface features, relatively low velocities representing interbedded Tertiary sediments and volcanics, and a deep high-velocity anomaly that may represent the root of an igneous intrusion, are mapped. Wide-angle reflections from the Moho are used to determine the thickness of the crust. The Moho is at 29 km depth beneath the east coast of the Queen Charlotte Islands. This is deeper than the Moho observed below Queen Charlotte Sound and as deep as, or deeper than, that below Hecate Strait. Crustal thinning during Tertiary extension was thus greatest beneath the surface expression of the Queen Charlotte Basin, leaving the crust under the islands considerably thicker than under the basin. In an alternate or additional explanation, compression at the continental margin during the last 4 Ma may have been taken up by thickening or underplating of the continental crust beneath the islands. If the Pacific plate is subducting beneath the islands, the Moho observations constrain the slab to dip greater than 20–26°.

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A three-dimensional crustal model of southwest Germany derived from seismic refraction data

Tectonophysics ◽

10.1016/0040-1951(87)90294-0 ◽

1987 ◽

Vol 142 (1) ◽

pp. 49-70 ◽

Cited By ~ 54

Author(s):

D. Gajewski ◽

W.S. Holbrook ◽

C. Prodehl

Keyword(s):

Seismic Refraction ◽

Three Dimensional ◽

Crustal Model ◽

Seismic Refraction Data ◽

Refraction Data ◽

Southwest Germany

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Seismic Refraction Data Analysis Using Machine Learning and Numerical Modeling for Characterization of Dam Construction Sites

Geophysics ◽

10.1190/geo2020-0935.1 ◽

2021 ◽

pp. 1-32

Author(s):

Rashed Poormirzaee ◽

Babak Sohrabian ◽

Pejman Tahmasebi

Keyword(s):

Machine Learning ◽

Neural Networks ◽

Prior Information ◽

Seismic Refraction ◽

P Wave ◽

Model Parameters ◽

Travel Times ◽

Number Of Layers ◽

Seismic Refraction Data ◽

Refraction Data

Seismic refraction is a cost-effective tool to reveal subsurface P-wave velocity. Inversion of travel times for estimating a realistic velocity model is a significant step in the processing of seismic refraction data. The results of the seismic data inversion are stochastic and, thus, using prior information or complementary geophysical data can have a significant role in estimating the structural properties based on observed data. Nevertheless, sufficient prior information or auxiliary data are not available in many geophysical sites. In such situations, developing advanced computational modeling is a vital step in providing primary information and improving the results. To this aim, a new inversion framework through hybrid committee artificial neural networks (CANN) and the flower pollination (FP) optimization algorithm is introduced for inversion of refracted seismic travel times. Synthetic models generated by a forward modeling approach are used to train the machine learning model. Then, model parameters, such as the number of layers, thicknesses, and P-wave velocities, are predicted using a committee machine constructed based on several neural networks, which is achieved by averaging and stack generalization methods where the latter method provides a better result. Then, the CANN results are used in the FP inversion algorithm to estimate the final model as it provides essential prior information on the number of layers and model parameters, which can be used in the FP searching algorithm. The proposed inversion procedure is tested on different synthetic datasets and applied at a dam site to determine the number of layers and their thicknesses. Our findings indicate a successful performance on both synthetic and real data for automatic inversion of seismic refraction data.

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An investigation into the time term method in refraction seismology

Bulletin of the Seismological Society of America ◽

10.1785/bssa0600010001 ◽

1970 ◽

Vol 60 (1) ◽

pp. 1-13

Author(s):

Leon Reiter

Keyword(s):

Seismic Refraction ◽

Three Dimensional ◽

Underlying Structure ◽

Model Studies ◽

Three Dimensional Representation ◽

Seismic Experiment ◽

Error Terms ◽

Time Term ◽

Seismic Refraction Data ◽

Refraction Data

abstract The time term method of seismic refraction data analysis allows an areal arrangement of shot points and stations and yields directly a three-dimensional representation of underlying structure. This method was investigated analytically and through numerical experiments to determine implicit sources of error and to provide guidelines for its proper use. Error terms for computed refractor depths were derived for two site arrays over two structures, a simply dipping refractor surface and a symmetric anticlinal refractor surface. These error terms proved to be qualitatively reliable guides to the performance of the time term method using models of multi site arrays over planar and biplanar refractor structures. Neither continuity of time terms nor use of a known refractor velocity in the computations offered a guarantee of a more accurate refractor reconstruction. In the two models tested a refractor velocity greater than the true velocity yielded the best reconstruction. Sensitivity to angle of dip indicated preferred orientation of shot-station lines along gentle apparent dips when the underlying structure is known and their orientation along several azimuths when the structure is unknown so as to mute the effect of high dip angles. If the structure has refractor surfaces dipping more than a few degrees, the time term method will give inaccurate results unless previous knowledge of the refractor configuration permits model studies to determine error terms and arrangement of shots and stations. Unfortunately such knowledge is usually the goal of a seismic experiment.

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