Seismic Velocity Distribution Research Articles

Electrical and seismological structure of the martian mantle and the detectability of impact-generated anomalies

We derive synthetic electrical conductivity, seismic velocity, and density distributions from the results of martian mantle convection models affected by basin-forming meteorite impacts. The electrical conductivity features an intermediate minimum in the strongly depleted topmost mantle, sandwiched between higher conductivities in the lower crust and a smooth increase toward almost constant high values at depths greater than 400km. The bulk sound speed increases mostly smoothly throughout the mantle, with only one marked change at the appearance of β-olivine near 1100km depth. An assessment of the detectability of the subsurface traces of an impact suggests that its signature would be visible in both observables at least if efficient melt extraction from the shock-molten target occurs, but it will not always be particularly conspicuous even for large basins; observations with extensive spatial and temporal coverage would improve their detectability. Electromagnetic sounding may offer another possibility to investigate the properties of the mantle, especially in regions of impact structures. In comparison with seismology and gravimetry, its application to the martian interior has received little consideration so far. Of particular interest is its potential for constraining the water content of the mantle. By comparing electromagnetic sounding data of an impact structure with model predictions, it might also be possible to answer the open question of the efficiency of extraction of impact-generated melt.

Time-Dependent Monitoring of Seismic Wave Velocity Variation Associated with Three Major Seismic Events at a Deep, Narrow-Vein Mine

One of the most difficult challenges in underground mining is to forecast significant seismic events prior to their occurrence in order to support the safety of miners and to minimize damage to the underground operation. Passive seismic tomography is a tool to image the seismic velocity changes in a rockmass, which can potentially reveal the rockmass behavior before and after a significant seismic event. In this paper, the changes in seismic velocity of the rockmass before and after three major seismic events are investigated to determine whether there are identifiable precursory velocity changes associated with the major seismic events. Conventional mechanics imply that the induced stress at the hypocenter would continue increasing until failure, in the form of an induced seismic event, occurs. With passive seismic tomography we can image changes to the seismic wave velocity distribution within a rockmass and hence infer the changes to the induced stress near the hypocenter. This paper evaluates the hypothesis that induced stress at the hypocenter (as inferred by the p-wave velocity) increases until the seismic event occurs. In addition to analyzing p-wave velocity changes near the hypocenter, changes to the p-wave velocity at “zone centers” were also analyzed. These “zone centers” are regions within the rockmass that consistently have a p-wave velocity that is much higher than the average p-wave velocity for the rockmass. It is found that the p-wave velocity did not increase at any of the three hypocenters prior to the seismic event occurring, however the p-wave velocity did increase in the closest “zone center” for two of the three events.

Numerical Simulations of Terrestrial Heat Flow in the Beiras Region, Mainland Portugal

Numerical simulations of heat flow density have been made for ten localities in the Beiras region of central Portugal where observational data are absent. The procedure adopted is based on results of deep crustal geophysical surveys and consider that the heat flow measured at the surface of the Earth results from the addition of heat generated in the crust by radioactive sources to that coming from the mantle. Radioactive heat sources in the region are heterogeneous and heat flow values at the surface depends on the thickness of upper crustal layers. Geotherms were obtained considering heat flow by conduction in the vertical direction. The models employed make use of data derived from geophysical surveys of Moho depths and detailed results related with seismic velocity distribution in the crust. In addition, results of radiometric surveys were employed in deriving heat production values for upper layers of the crust. A value around 35 mW m-2 was assumed for heat flow from the mantle. The resulting heat flow density values are similar to those found for areas with similar tectonic characteristics in NW Africa and in Southern Portugal.

Using Shallow Seismic Method for Evaluation of the Foundation Beds of New Cairo Extension (Andalus Area), Egypt.

Shallow Seismic Refraction Method (SSR) in engineering investigation is growing interest after the October 1992 earthquake in Egypt. In the present study, eight shallow seismic refraction (SSR) profiles were acquired along the Al-Andalus area, which located at the southeastern part of new Cairo extension, Egypt, in order to identify the shallow subsurface geological features of the near-surface section. Both Primary (VP)-wave and Secondary (VS)-wave velocities that were picking and computed during processing and interpretation. The seismic compressional wave velocity (Vp) distribution indicates that there are three geoseismic layers ranging between (420 and 680 m/s), (1040 and 1680 m/s) and (2170 and 3100 m/s), for first, second and third layers, respectively. The first shear wave velocity (VS) is ranging between (240 – 390 m/s), the second VS layer ranging between (570 - 980 m/s), and the third VS layer is ranging between (1240 - 1800 m /s). The thickness of the first layer varies from 1.8 to 2.6 m and the second layer ranges between 7.6 and 10.5 m. The geoseismic cross sections are interpreted geologically as the first low velocity values which indicate weathered sediments fine sands change to sandy gravels sometimes. However, the second geoseismic layer is represented by consolidated sands with clay intercalations and the third layer reflected sandstones. The geotechnical parameters (elastic modulus, material competence and bearing capacities) are estimated. The distribution of these parameters noticed that the areas can be carried heavy loads at the central, east central and north central parts of the study area.

Assessment of the geoenvironment stress state at the Caucasian mineral waters test plot using long-term seismic-ecological monitoring

According to the results of continuous long-term seismic-ecological monitoring at the Caucasian Mineral Waters test plot (the seismic zone in the Cis-Elbrus region), data on the seismic velocity distribution pattern were obtained for the test plot territory. The high-speed structure is revealed, the horizontal dimensions of which do not allow predicting local earthquakes with a very high magnitude in this territory. Three-dimensional models of anisotropy index γ were obtained and the indexes of stress state S were estimated for different depths according to the interpretation results of converted PS waves from distant earthquakes. It is found that the distribution of the anisotropy index γ varies continuously by the depth, by the laterals and in time. The cyclic changes in the index S with time are noted for all depths.

Landslide Analysis Using Seismic Refraction Tomography And MASW: a Case Study in Ponorogo, East Java, Indonesia

Ponorogo district morphology form consisting of highlands and hills make this area vulnerable to landslides. Based on the BNPB (National Disaster Management Agency) data from 2013 to 2017, 77 landslides and 35% have occurred in Ngrayun and Slahung sub-districts. One area that has the potential to experience landslides is Tugurejo village in Slahung District. This study aims to determine the physical properties of subsurface rocks using SRT (Seismic Refraction Tomography) and MASW (Multi-channel Analysis of Surface Waves). The seismic velocity distribution defined from the SRT and MASW at the study sites shows a zone with a higher porosity that is interpreted to represent the level and depth of rock mass movement. P-wave velocity and S-wave indicates very low velocity of 500 – 1200 m/s and 100 – 250 m/s at depths up to 5 m .

Landslide Analysis Using Seismic Refraction Tomography And MASW: a Case Study in Ponorogo, East Java, Indonesia

Ponorogo district morphology form consisting of highlands and hills make this area vulnerable to landslides. Based on the BNPB (National Disaster Management Agency) data from 2013 to 2017, 77 landslides and 35% have occurred in Ngrayun and Slahung sub-districts. One area that has the potential to experience landslides is Tugurejo village in Slahung District. This study aims to determine the physical properties of subsurface rocks using SRT (Seismic Refraction Tomography) and MASW (Multi-channel Analysis of Surface Waves). The seismic velocity distribution defined from the SRT and MASW at the study sites shows a zone with a higher porosity that is interpreted to represent the level and depth of rock mass movement. P-wave velocity and S-wave indicates very low velocity of 500 – 1200 m/s and 100 – 250 m/s at depths up to 5 m .

Fault‐Associated Magma Conduits Beneath Volcán de Colima Revealed by Seismic Velocity and Attenuation Tomography Studies

AbstractWe present the results of tomographic studies using seismic velocity and attenuation in the area of the Colima Volcanic complex (CVC). Our dataset comprises body waves from local earthquakes recorded by the temporary seismic stations of the CODEX network in the Colima area and a few stations of the regional Mapping the Rivera Subduction Zone (MARS) networks, both deployed in 2006–2008. We obtain three‐dimensional distributions of seismic velocities and attenuation in the crust beneath the CVC area. At shallow depths, we observe a large negative anomaly to the south of CVC, coinciding with the location of the Central Colima Graben. This anomaly may represent debris avalanche deposits, as well as shallow magma reservoirs feeding the eruptions of the presently active Volcán de Colima. In contrast, the volcano edifice of Nevado de Colima, which is built of rigid igneous rocks, is associated with high‐velocity and low‐attenuation anomalies at shallow depths. In the deeper section, a major anomaly with high Vp/Vs, low Vs, and high S wave attenuation corresponds to the location of the regional Tamazula fault. As this represents a mechanically weakened zone of the crust, it may form the pathway that feeds CVC. Both velocity and attenuation models show that the fault‐associated conduit brought magma from the mantle through the lower crust to a depth of 15 km. Then, a light fraction of magma may continue to ascend, forming shallow reservoirs beneath the southern flank of CVC.

Ionian Abyssal Plain: a window into the Tethys oceanic lithosphere

Abstract. The nature of the Ionian Sea crust has been the subject of scientific debate for more than 30 years, mainly because seismic imaging of the deep crust and upper mantle of the Ionian Abyssal Plain (IAP) has not been conclusive to date. The IAP is sandwiched between the Calabrian and Hellenic subduction zones in the central Mediterranean. A NNE–SSW-oriented 131 km long seismic refraction and wide-angle reflection profile, consisting of eight ocean bottom seismometers and hydrophones, was acquired in 2014. The profile was designed to univocally confirm the proposed oceanic nature of the IAP crust as a remnant of the Tethys and to confute its interpretation as a strongly thinned part of the African continental crust. A P-wave velocity model developed from travel-time forward modelling is refined by gravimetric data and synthetic modelling of the seismic data. A roughly 6–7 km thick crust with velocities ranging from 5.1 to 7.2 km s−1, top to bottom, can be traced throughout the IAP. In the vicinity of the Medina seamounts at the southern IAP boundary, the crust thickens to about 9 km and seismic velocities decrease to 6.8 km s−1 at the crust–mantle boundary. The seismic velocity distribution and depth of the crust–mantle boundary in the IAP document its oceanic nature and support the interpretation of the IAP as a remnant of the Tethys lithosphere with the Malta Escarpment as a transform margin and a Tethys opening in the NNW–SSE direction.

3-D seismic travel-time tomography validation of a detailed subsurface model: a case study of the Záncara river basin (Cuenca, Spain)

Abstract. A high-resolution seismic tomography survey was acquired to obtain a full 3-D P-wave seismic velocity image in the Záncara river basin (eastern Spain). The study area consists of lutites and gypsum from a Neogene sedimentary sequence. A regular and dense grid of 676 shots and 1200 receivers was used to image a 500 m×500 m area of the shallow subsurface. A 240-channel system and a seismic source, consisting of an accelerated weight drop, were used in the acquisition. Half a million travel-time picks were inverted to provide the 3-D seismic velocity distribution up to 120 m depth. The project also targeted the geometry of the underground structure with emphasis on defining the lithological contacts but also the presence of cavities and fault or fractures. An extensive drilling campaign provided uniquely tight constraints on the lithology; these included core samples and wireline geophysical measurements. The analysis of the well log data enabled the accurate definition of the lithological boundaries and provided an estimate of the seismic velocity ranges associated with each lithology. The final joint interpreted image reveals a wedge-shaped structure consisting of four different lithological units. This study features the necessary key elements to test the travel time tomographic inversion approach for the high-resolution characterization of the shallow subsurface. In this methodological validation test, travel-time tomography demonstrated to be a powerful tool with a relatively high capacity for imaging in detail the lithological contrasts of evaporitic sequences located at very shallow depths, when integrated with additional geological and geophysical data.

Geophysical surveys for the dynamic characterization of a cultural heritage building and its subsoil: The S. Michele Arcangelo Church (Acireale, eastern Sicily)

Abstract Geophysical surveys are useful tools to characterize the buildings making up the cultural heritage and to monitor the subsoil features on which they are constructed. The information obtained is necessary for planning future restoration work. The aim of this study is to characterize the dynamic features of both the San Michele Arcangelo Church and of the area where it is located. Non-invasive geophysical surveys, including electromagnetic and seismic surveys, were performed to acquire this information. Such techniques enabled us to highlight the seismic wave velocity distribution in the subsoil, and the presence of electromagnetic reflectors probably linked to the existence of remains belonging to the old edifice. The comparison and integration of different methods allowed us to validate the results. Moreover, ambient seismic noise measurements were carried out outside and inside the church to obtain information on the site resonance frequency and to assess the vibration frequencies of the church. The results do not point out any site amplifications in the vibration frequency range of the church. It is therefore unlikely that soil-to-structure resonance phenomena can take place.

Full Waveform Inversion for Advance Exploration of Ground Properties in Mechanized Tunneling

We present a new approach for exploration of small- and large-scale geological structures in mechanized tunneling environments by analyzing actively excited seismic waves illuminating the soil in front of the tunnel-boring machine. Applying the concept of full waveform inversion, we exploit all information contained in the seismic recordings to image unknown disturbances of soil properties along the tunnel track. Owing to the lack of field data, we explore two-dimensional synthetic test models containing exemplary disturbances of the soil, where real recordings are replaced by synthetic ones obtained by solving the (an)elastic wave equation with a Nodal Discontinuous Galerkin method. An extension to three dimensions is straight forward but computationally expensive. Disturbances in these test models are reconstructed with an iterative procedure guided by minimization of the misfit between measured and predicted records. Our method is validated by means of a simple test case and different minimization procedures including a quasi-Newton method are compared. The presented method is able to reconstruct the spatial distribution of seismic wave velocities (P and S waves) and can detect large and small-scale objects ahead of the tunnel face characterized by wave velocities differing from that of the surrounding bedrock. The imaging process is stabilized by a multiscale approach, where the frequency content of the recordings is successively extended with the number of iterations. Incorporating viscoelastic attenuation of the surrounding bedrock does not compromise the capability of detecting large-scale objects as long as low-frequency waves are used.

Extrapolation of bulk rock elastic moduli of different rock types to high pressure conditions and comparison with texture-derived elastic moduli

In this study elastic moduli of three different rock types of simple (calcite marble) and more complex (amphibolite, micaschist) mineralogical compositions were determined by modeling of elastic moduli using texture (crystallographic preferred orientation; CPO) data, experimental investigation and extrapolation. 3D models were calculated using single crystal elastic moduli, and CPO measured using time-of-flight neutron diffraction at the SKAT diffractometer in Dubna (Russia) and subsequently analyzed using Rietveld Texture Analysis. To define extrinsic factors influencing elastic behaviour, P-wave and S-wave velocity anisotropies were experimentally determined at 200, 400 and 600 MPa confining pressure. Functions describing variations of the elastic moduli with confining pressure were then used to predict elastic properties at 1000 MPa, revealing anisotropies in a supposedly crack-free medium. In the calcite marble elastic anisotropy is dominated by the CPO. Velocities continuously increase, while anisotropies decrease from measured, over extrapolated to CPO derived data. Differences in velocity patterns with sample orientation suggest that the foliation forms an important mechanical anisotropy. The amphibolite sample shows similar magnitudes of extrapolated and CPO derived velocities, however the pattern of CPO derived velocity is closer to that measured at 200 MPa. Anisotropy decreases from the extrapolated to the CPO derived data. In the micaschist, velocities are higher and anisotropies are lower in the extrapolated data, in comparison to the data from measurements at lower pressures. Generally our results show that predictions for the elastic behavior of rocks at great depths are possible based on experimental data and those computed from CPO. The elastic properties of the lower crust can, thus, be characterized with an improved degree of confidence using extrapolations. Anisotropically distributed spherical micro-pores are likely to be preserved, affecting seismic velocity distributions. Compositional variations in the polyphase rock samples do not significantly change the velocity patterns, allowing the use of RTA-derived volume percentages for the modeling of elastic moduli.

A Shallow Seismic Velocity Model for the Groningen Area in the Netherlands

AbstractThe province of Groningen in the Netherlands holds one of the world's largest natural gas fields, and it has been an important source of energy for Western Europe for many decades. The seismicity in recent years called for a better understanding of the local subsurface, and therefore a dense network of 70 boreholes was installed in early 2015. Each borehole is equipped with four geophones and a surface accelerometer. In this study, data from this network are used to determine the shallow velocity structure that is important for the quantification of the seismic hazard and accurate source localizations. Compressional and shear wave velocity profiles with uncertainties are derived for each of the 200 m deep boreholes using passive seismic interferometry applied to local event data. The resulting seismic velocity distributions are presented as contour maps for 50 m depth intervals. The maps show strong lateral variations, where areas of low VP/VS ratio correspond to regions of sedimentary infill. The shear wave velocities were derived using the transverse component seismograms. Because the sensor orientations of the borehole geophones were unknown, they had to be determined first. This was done using a novel method based on cross correlations between the geophones and their colocated surface accelerometer. In addition, by extensive cross‐correlation analysis over the network, several installation inconsistencies were identified and resolved.

Special features of distribution of seismic waves propagation velocity in the Earth crust in the area of uranium deposits (Kirovograd ore area of Ingul megablock of the Ukrainian Shield)

Special features of distribution of seismic waves propagation velocity in the Earth crust in the area of uranium deposits (Kirovograd ore area of Ingul megablock of the Ukrainian Shield)

A monodisperse microspheres/silk fibroin nanofiber composite with controlled release of biomolecules for vascular tissue engineering

In this study elastic moduli of three different rock types of simple (calcite marble) and more complex (amphibolite, micaschist) mineralogical compositions were determined by modeling of elastic moduli using texture (crystallographic preferred orientation; CPO) data, experimental investigation and extrapolation. 3D models were calculated using single crystal elastic moduli, and CPO measured using time-of-flight neutron diffraction at the SKAT diffractometer in Dubna (Russia) and subsequently analyzed using Rietveld Texture Analysis. To define extrinsic factors influencing elastic behaviour, P-wave and S-wave velocity anisotropies were experimentally determined at 200, 400 and 600 MPa confining pressure. Functions describing variations of the elastic moduli with confining pressure were then used to predict elastic properties at 1000 MPa, revealing anisotropies in a supposedly crack-free medium. In the calcite marble elastic anisotropy is dominated by the CPO. Velocities continuously increase, while anisotropies decrease from measured, over extrapolated to CPO derived data. Differences in velocity patterns with sample orientation suggest that the foliation forms an important mechanical anisotropy. The amphibolite sample shows similar magnitudes of extrapolated and CPO derived velocities, however the pattern of CPO derived velocity is closer to that measured at 200 MPa. Anisotropy decreases from the extrapolated to the CPO derived data. In the micaschist, velocities are higher and anisotropies are lower in the extrapolated data, in comparison to the data from measurements at lower pressures. Generally our results show that predictions for the elastic behavior of rocks at great depths are possible based on experimental data and those computed from CPO. The elastic properties of the lower crust can, thus, be characterized with an improved degree of confidence using extrapolations. Anisotropically distributed spherical micro-pores are likely to be preserved, affecting seismic velocity distributions. Compositional variations in the polyphase rock samples do not significantly change the velocity patterns, allowing the use of RTA-derived volume percentages for the modeling of elastic moduli.

3-D crustal velocity structure of western Turkey: Constraints from full-waveform tomography

The Sea of Marmara and western Turkey are characterized by intense seismicity and crustal deformation due to transition tectonics between the North Anatolian Fault Zone (NAFZ) and the extensional Aegean. Seismic imaging of the crust and uppermost mantle in W-NW Turkey is crucial to obtain a better understanding of its seismotectonics and geodynamics. So far, the Sea of Marmara and surroundings were considered in various active and passive seismic experiments providing significant information on crustal properties. Here, we further investigate the 3-D seismic velocity structure in this rapidly deforming region using non-linear full-waveform tomography based on the adjoint method. Our model is constrained by complete waveforms of 62 regional earthquakes (epicentral distance<10°) with magnitudes Mw≥3.7, which occurred between 2007 and 2015. Validation tests show that our final 3-D Earth model is able to explain seismic waveforms from earthquakes not used in the inversion at periods from 8-100s to within the data uncertainties. Furthermore, quantitative resolution analyses yield 15 to 35km horizontal resolution lengths in the shallow and deep crust beneath well-covered areas of W-NW Turkey. Our full-waveform tomography results indicate the presence of strong lateral and vertical velocity variations (2.55≤VS≤4.0km/s) down to depths of ∼35km. The seismic velocity distribution is characteristic of highly deformed and distributed crustal features along major fault zones (e.g. NAFZ and its branches), historic and recent regional volcanism (e.g. Kula volcanic province), and metamorphic core complex developments (e.g. Menderes and Kazdağ massifs). Radial anisotropy is very strong (around 20%) throughout the crust, further attesting to strong deformation and heterogeneity. Generally, our 3-D model is overall consistent with the active tectonics of western Turkey.

Variations in seismic velocity distribution along the Ryukyu (Nansei-Shoto) Trench subduction zone at the northwestern end of the Philippine Sea plate

The Ryukyu (Nansei-Shoto) island arc-trench system, southwest of Japan, is formed by the subduction of the Philippine Sea (PHS) plate. Among the subduction zones surrounding the Japan Islands, the Ryukyu arc-trench system is unique in that its backarc basin, the Okinawa Trough, is the area with current extensively active rifting. The length of the trench is around 1400 km, and the geological and geophysical characteristics vary significantly along the trench axis. We conducted multichannel seismic (MCS) reflection and wide-angle seismic surveys to elucidate the along-arc variation in seismic structures from the island arc to the trench regions, shooting seven seismic lines across the arc-trench system and two along-arc lines in the island arc and the forearc areas. The obtained P-wave velocity models of the Ryukyu arc crust were found to be heterogeneous (depending on the seismic lines), but they basically consist of upper, middle, and lower crusts, indicating a typical island arc structure. Beneath the bathymetric depressions cutting the island arc—for example, the Kerama Gap and the Miyako Saddle—the MCS record shows many across-arc normal faults, which indicates the presence of an extensional regime along the island arc. In the areas from the forearc to the trench, the subduction of the characteristic seafloor features on the PHS plate affects seismic structures; the subducted bathymetric high of the Amami Plateau is detected in the northern trench: the Luzon–Okinawa fracture zone beneath the middle and southern trenches. There are low-velocity (<~4.5 km/s) wedges along the forearc areas, except for off Miyako-jima Island. The characteristic high gravity anomaly at the forearc off Miyako-jima Island is caused not by a bathymetric high of a large-scale accretionary wedge but by shallower materials with a high P-wave velocity of ~4.5 km/s.Graphical Position of the seismic survey lines in the Ryukyu arc-trench system (right) and P-wave velocity models for the lines perpendicular to the trench axis (left). The contour interval is 2.5 km/s. The vertical blue line shows the position of the trench axis.

THE REACTION OF PHYSICAL TRANSFORMATION OF THE GRAVITY DATA AND LINEARITY DILEMMA

This paper consists of opinions on the article entitled as “Investigation of the Seismic Velocity Distribution and Crustal Structure of Turkey by means of Gravity Data” which was published on the page 185 of the 153rd issue of the Bulletin of Mineral Research and Exploration. Within this context, it was aimed at defining some dilemmas encountered in the article, which was targeted in the exploration of the crustal structure in plate scale by means of data sets, and informing the reader. Here, the interactive relationships of Gravity and Seismic methods of which each one are discipline of expertise will be studied within scope of the mentioned article.

Role of the Taratash indenter in the Ural mountains building

The article presents the new data concerning the bounding zones of the Archean - Early Proterozoic Taratash block. It breaks the longitude structure of the Urals, squeezing all structural zones at a latitude of the town Miass. There were studied the meso- and microstructures of the boundary zones, anisotropy of magnetic susceptibility of faulted rocks and distribution of seismic waves velocities in to blastomylonites. We suggest that kinematic history of the Taratash block consists of two phases: 1) Middle Riphean exhumation of Taratash rocks in tension environ- ment; 2) Late Paleozoic formation of Indenter due regional shortening setting.