3-D crustal VS model of western France and the surrounding regions using Monte-Carlo inversion of seismic noise cross-correlation dispersion diagrams

Summary Due to a too sparse permanent seismic coverage during the last decades, the crustal structure of western France and the surrounding regions is poorly known. In this study, we present a 3-D seismic tomographic model of this area obtained from the analysis of 2-year continuous data recorded from 55 broad-band seismometers. An unconventional approach is used to convert Rayleigh wave dispersion diagrams obtained from ambient noise cross-correlations into posterior distributions of 1-D VS models integrated along each station pair. It allows to avoid the group velocity map construction step (which means dispersion curve extraction) while providing meaningful VS posterior uncertainties. VS models are described by a self-adapting and parsimonious parameterization using cubic Bézier splines. 1268 separately inverted 1-D VS profiles are combined together using a regionalization scheme, to build the 3-D VS model with a lateral resolution of 75 km over western France. The shallower part of the model (horizontal cross-section at 4 km depth) correlates well with the known main geological features. The crystalline Variscan basement is clearly associated with positive VS perturbations while negative heterogeneities match the Mesocenozoic sedimentary basins. At greater depths, the Bay of Biscay exhibits positive VS perturbations,which eastern and southern boundaries can be interpreted as the ocean-continent transition. The overall crustal structure below the Armorican Massif appears to be heterogenous at the subregional scale, and tends to support that both the South-Armorican Shear Zone and the Paris Basin Magnetic Anomaly are major crustal discontinuities that separate distinct domains.

Download Full-text

SURFACE‐WAVE DISPERSION APPLIED TO THE DETECTION OF SEDIMENTARY BASINS

Geophysics ◽

10.1190/1.1440514 ◽

1975 ◽

Vol 40 (1) ◽

pp. 40-55 ◽

Cited By ~ 8

Author(s):

Robert H. Tatham

Keyword(s):

Surface Wave ◽

Crustal Structure ◽

Gulf Coast ◽

Sedimentary Basins ◽

Wave Dispersion ◽

Petroleum Exploration ◽

Underground Nuclear Explosion ◽

Surface Wave Dispersion ◽

Mississippi Embayment ◽

Model Calculations

Seismic surface‐wave velocities are greatly affected by crustal structure. Because there is a strong contrast in the physical properties of clastic sediments and underlying basement materials, surface‐wave dispersion provides a fast, convenient, and inexpensive means of detecting sedimentary basins and estimating their thickness. Model calculations and published reports of explosion studies indicate that sedimentary thicknesses as shallow as 500 m (∼1650 ft) should be detectable by analysis of routinely recorded earthquake seismograms. This study demonstrates the use of seismic surface‐wave dispersion to detect sedimentary basins and to estimate their thickness. The technique is used first for the Mississippi embayment region of the U.S. Gulf Coast, where the crustal structure is known and the results can be verified, and then applied to offshore Greenland, where the crustal structure is unmapped but a sedimentary basin is suspected. The data used are available seismograms of natural earthquakes and, for the Gulf Coast area, an underground nuclear explosion. Because this technique requires only existing, readily available data and may be applied to many regions of the world, it offers an attractive reconnaissance tool in petroleum exploration. In the present study, surface‐wave dispersion and the effects of shallow crustal structure are reviewed in light of this application, and the advantages and limitations of the technique are explored.

Download Full-text

Spurious low velocity zones in joint inversions of surface waves and receiver functions

Geophysical Journal International ◽

10.1093/gji/ggz345 ◽

2019 ◽

Vol 219 (2) ◽

pp. 1032-1042

Author(s):

Chao Gao ◽

Erin Cunningham ◽

Vedran Lekić

Keyword(s):

Surface Wave ◽

Crustal Structure ◽

Receiver Function ◽

Model Space ◽

Sedimentary Basins ◽

Wave Dispersion ◽

Receiver Functions ◽

Low Velocity ◽

Surface Wave Dispersion ◽

Surface Wave Data

SUMMARY Low-velocity layers within the crust can indicate the presence of melt and lithologic differences with implications for crustal composition and formation. Seismic wave conversions and reverberations across the base of the crust or intracrustal discontinuities, analysed using the receiver function method, can be used to constrain crustal layering. This is commonly accomplished by inverting receiver functions jointly with surface wave dispersion. Recently, the proliferation of model-space search approaches has made this technique a workhorse of crustal seismology. We show that reverberations from shallow layers such as sedimentary basins produce spurious low-velocity zones when inverted for crustal structure with surface wave data of insufficiently high frequency. Therefore, reports of such layers in the literature based on inversions using receiver function data should be re-evaluated. We demonstrate that a simple resonance-removal filter can suppress these effects and yield reliable estimates of crustal structure, and advocate for its use in receiver-function based inversions.

Download Full-text

Twin enigmatic microseismic sources in the Gulf of Guinea observed on intercontinental seismic stations

Geophysical Journal International ◽

10.1093/gji/ggt076 ◽

2013 ◽

Vol 194 (1) ◽

pp. 362-366 ◽

Cited By ~ 15

Author(s):

Yingjie Xia ◽

Sidao Ni ◽

Xiangfang Zeng

Keyword(s):

North America ◽

Temporal Variation ◽

Crustal Structure ◽

Source Region ◽

Broad Band ◽

Active Volcano ◽

Gulf Of Guinea ◽

Waveform Data ◽

Seismic Stations ◽

The Earth

Abstract Based on studies of continuous waveform data recorded on broad-band seismograph stations in Africa, Europe and North America, we report evidences for two temporally persistent and spatially localized monochromatic vibrating sources (around 0.036 and 0.038 Hz, respectively) in the Gulf of Guinea, instead of just one source (0.038 Hz or 26 s) found 50 yr ago. The location of the 0.036 Hz source is close to the Sao Tome Volcano, therefore it may be related to volcano processes. However, the 0.038 Hz source cannot be explained with known mechanisms, such as tectonic or oceanic processes. The most likely mechanism is volcano processes, but there is no reported active volcano in source region. Such repetitive vibration sources may provide valuable tools for detecting temporal variation of crustal structure of the Earth.

Download Full-text

Major geological features and lateral variation of crustal structure in southern New England

Tectonophysics ◽

10.1016/0040-1951(90)90145-x ◽

1990 ◽

Vol 178 (2-4) ◽

pp. 183-192

Author(s):

Alan L. Kafka ◽

James W. Skehan

Keyword(s):

New England ◽

Crustal Structure ◽

Lateral Variation ◽

Southern New England ◽

Geological Features

Download Full-text

Ambient noise cross-correlation observations of fundamental and higher-mode Rayleigh wave propagation governed by basement resonance

10.26686/wgtn.13818893.v1 ◽

2021 ◽

Author(s):

Martha Savage ◽

FC Lin ◽

John Townend

Keyword(s):

Rayleigh Wave ◽

Correlation Functions ◽

Rayleigh Waves ◽

Ambient Noise ◽

Cross Correlation ◽

Amplitude Ratio ◽

Sedimentary Basins ◽

Longitudinal Motion ◽

Resonance Frequencies ◽

Noise Cross Correlation

Measurement of basement seismic resonance frequencies can elucidate shallow velocity structure, an important factor in earthquake hazard estimation. Ambient noise cross correlation, which is well-suited to studying shallow earth structure, is commonly used to analyze fundamental-mode Rayleigh waves and, increasingly, Love waves. Here we show via multicomponent ambient noise cross correlation that the basement resonance frequency in the Canterbury region of New Zealand can be straightforwardly determined based on the horizontal to vertical amplitude ratio (H/V ratio) of the first higher-mode Rayleigh waves. At periods of 1-3 s, the first higher-mode is evident on the radial-radial cross-correlation functions but almost absent in the vertical-vertical cross-correlation functions, implying longitudinal motion and a high H/V ratio. A one-dimensional regional velocity model incorporating a ~ 1.5 km-thick sedimentary layer fits both the observed H/V ratio and Rayleigh wave group velocity. Similar analysis may enable resonance characteristics of other sedimentary basins to be determined. © 2013. American Geophysical Union. All Rights Reserved.

Download Full-text

Short-period surface-wave dispersion and shallow crustal structure of central and eastern Tennessee

Bulletin of the Seismological Society of America ◽

10.1785/bssa0820020962 ◽

1992 ◽

Vol 82 (2) ◽

pp. 962-979

Author(s):

Paul C. Yao ◽

James Dorman

Keyword(s):

Surface Wave ◽

Half Space ◽

Crustal Structure ◽

Group Velocity Dispersion ◽

Wave Dispersion ◽

Surface Wave Dispersion ◽

Zero Crossing ◽

Clastic Rocks ◽

Dispersion Data ◽

Short Period

Abstract Group velocity dispersion of explosion-generated seismic surface waves with periods ranging from 0.2 to 1.5 sec is used to investigate shallow crustal structure of eastern and central Tennessee. Several modes of both Rayleigh and Love waves can be identified and separated on the seismograms of seven SARSN regional network stations by zero-phase digital filtering. Dispersion data for sinusoidal wave motion were based on digitized zero-crossing times. By forward modeling, we find that a wave guide of at least two layers over a half-space can adequately represent our particular multi-mode, narrow-band observations. In a layered section about 3 km thick, lower velocities characterize outcropping clastic rocks of the Cumberland plateau, and higher velocities correspond to shallow carbonate rocks of the Nashville Dome. Half-space shear velocities of about 3.9 km/sec appear to represent lower Paleozoic carbonate lithology deeper than 2 to 4 km on most of the observed paths. Our best data, interpreted jointly with earlier data of Oliver and Ewing (1958) and of Chen et al. (1989), have a composite period range of 0.2 to 40 sec, but they represent different Appalachian paths. Group velocities over this broad spectrum are satisfied by a complex model with two low-velocity layers. The uniqueness of this model cannot be demonstrated, but it represents important hypotheses concerning regional geologic features that can be tested more rigorously by improved surface-wave dispersion data.

Download Full-text

Crustal Structure from Joint Inversion of Receiver Function and Surface Wave Dispersion beneath Duhok, NW Iraq

10.1190/ist092012-001.14 ◽

2012 ◽

Cited By ~ 2

Author(s):

Wathiq Abdulnaby ◽

Hanan Mahdi ◽

Haydar Al-Shukri

Keyword(s):

Surface Wave ◽

Crustal Structure ◽

Receiver Function ◽

Joint Inversion ◽

Wave Dispersion ◽

Surface Wave Dispersion

Download Full-text

Crustal structures beneath the Eastern and Southern Alps from ambient noise tomography

10.5194/se-2019-177 ◽

2020 ◽

Author(s):

Ehsan Qorbani ◽

Dimitri Zigone ◽

Mark R. Handy ◽

Götz Bokelmann ◽

Keyword(s):

High Resolution ◽

Crustal Structure ◽

Ambient Noise ◽

Eastern Alps ◽

Southern Alps ◽

Ambient Noise Tomography ◽

Tauern Window ◽

Velocity Models ◽

Cross Correlations ◽

Velocity Anomalies

Abstract. We study the crustal structure under the Eastern and Southern Alps using ambient noise tomography. We use cross-correlations of ambient seismic noise between pairs of 71 permanent stations and 19 stations of the EASI profile to derive new high-resolution 3-D shear-velocity models for the crust. Continuous records from 2014 and 2015 are cross-correlated to estimate Green's functions of Rayleigh and Love waves propagating between the station pairs. Group velocities extracted from the cross-correlations are inverted to obtain isotropic 3-D Rayleigh and Love-wave shear-wave velocity models. Our high resolution models image several velocity anomalies and contrasts and reveal details of the crustal structure. Velocity variations at short periods correlate very closely with the lithologies of tectonic units at the surface and projected to depth. Low-velocity zones, associated with the Po and Molasse sedimentary basins, are imaged well to the south and north of the Alps, respectively. We find large high-velocity zones associated with the crystalline basement that forms the core of the Tauern Window. Small-scale velocity anomalies are also aligned with geological units such as the Ötztal and the Gurktal nappes of the Austroalpine nappes. Clear velocity contrasts in the Tauern Window along vertical cross-sections of the velocity model show the depth extent of the tectonic units and their bounding faults. A mid-crustal velocity contrast is interpreted as a manifestation of intracrustal decoupling in the Eastern Alps and decoupling between the Southern and Eastern Alps.

Download Full-text