High-velocity Layer Research Articles

Validating the origin of microseismic events in target reservoir using guided waves recorded by DAS

We develop a new algorithm that uses guided-wave energy in distributed acoustic sensing (DAS) records to identify microseismic events originating within or very close to a shale reservoir. Guided waves are dispersive waves that propagate in a low-velocity layer bounded by two high-velocity layers. This is a geologic structure that is seen for some shale reservoirs, most notably the Eagle Ford. Only microseismic events originating within or close to the low-velocity layer will excite significant guided-wave energy, which can be observed in DAS records. We confirm the relationship between guided-wave energy and event depth relative to the reservoir by using synthetic modeling. Given the known velocity structure, we can predict the dispersion curves for guided waves and use them to separate body and guided waves. We demonstrate a method to quantify the amplitude of guided waves in field DAS data recorded directly above the Eagle Ford Shale. Using this technique, we can separate events that originate within or close to the Eagle Ford from events that do not, thus circumventing the large depth uncertainty in a microseismic catalog derived from surface geophones. Our analysis shows that events classified as originating within or close to the Eagle Ford are horizontally closer to the stimulating well than non-Eagle Ford events. This is interpreted as representing different hydraulic fracture geometries in the Eagle Ford compared to its bounding formations, the Buda Limestone and Austin Chalk. The application of our method yields a new catalog that highlights the events relevant to stimulation and production in the target reservoir. It also provides a strong depth constraint that can improve relocation attempts using surface data, enabling a more accurate estimation of stimulated rock volume geometry.

Updated Antarctic crustal model

We use seismic data together with a subglacial bedrock relief from the BEDMAP2 database to obtain a new three-layer model of the consolidated (crystalline) crust of Antarctica that locally improves the global seismic crustal model CRUST1.0. We collect suitable data for constructing crustal layers, analyse them and build maps of the crustal layer thickness and seismic velocities. We use the subglacial relief according to a tectonic configuration and then interpolate data using a statistical kriging method. The P-wave velocity information from old seismic profiles have been supplemented with the new shear-wave velocity models. We adjust the thickness of crustal layers by multiplying a total crustal thickness by a percentage ratio of each individual layer at each point. Our results reveal large variations in seismic velocities between different crustal blocks forming Antarctica. The most pronounced differences exist between East and West Antarctica. In East Antarctica, a high P-wave velocity (vP > 7 km/s) layer in the lower crust is absent. The P-wave velocity in the lower crust changes from 6.1 km/s beneath the Lambert Rift to 6.9 km/s beneath the Wilkes Basin. In West Antarctica, a thick mafic lower crust is characterized by large P-wave velocities, ranging from 7.0 km/s under the Ross Sea to 7.3 km/s under the Byrd Basin. In contrast, velocities in the lower crust beneath the Transantarctic and Ellsworth-Whitmore Mountains are ~6.8 km/s. The P-wave velocities in the upper crust in East Antarctica are within the range 5.5–6.4 km/s. The upper crust of West Antarctica is characterized by the P-wave velocities of 5.6–6.3 km/s. The P-wave velocities in the middle crust vary within 5.9–6.6 km/s in East Antarctica and within 6.3–6.5 km/s in West Antarctica. A low-velocity layer (5.8–5.9 km/s) is detected at depth of ~20–25 km beneath the Princes Elizabeth Land.

Crustal velocity structure of the Northwest Sub-basin of the South China Sea based on seismic data reprocessing

The deep crustal structure of the Northwest Sub-basin (NWSB) of the South China Sea (SCS) is of great importance for understanding the tectonic nature of the continent-ocean transition (COT) and magmatism in this oceanic basin. The 2-D wide-angle reflection/refraction seismic profile OBS2006-2 is almost parallel to the extinct spreading ridge (ESR) of the NWSB. In addition to the original data, we added the data of two reprocessed OBS stations, and carried out seismic phase re-picking and travel-time imaging to obtain the crustal velocity structure along this profile. Resolution tests demonstrate that the newly acquired velocity structure is more reliable than the prior interpretation. The depth of the Moho (23.5–11.8 km) and crustal thickness (20.5–6.5 km) systematically changes from continental crust of the Xisha Block to the oceanic crust within the NWSB. The COT zone has a width of ∼20 km and the depth of the Moho decreases from 15.0 to 11.0 km, corresponding to a ∼4 km decrease in crustal thickness (6–10 km). A high velocity layer (HVL, 7.2–7.4 km s−1) exists at the bottom of the crust at the location where the sharp lateral transition of the continental crust to the oceanic crust occurs. Age dating shows that the Double-peak Seamount was formed at ∼23 Ma, after the cessation of the NWSB seafloor spreading (∼32-25 Ma). The crust beneath the Double-peak Seamount is oceanic with a thickness of 9 km. We infer that this oceanic crust was formed by magmatic upwelling and decompression melting along a pre-existing zone of weakness.

Imaging Subsurface Structure of an Urban Area Based on Diffuse-Field Theory Concept Using Seismic Ambient Noise

Single station ambient noise measurement in campaign mode has of late gained a huge popularity among geo-scientists. Herein, we present results of ambient vibration analysis, executed in a highly populated urban area covering 47 survey points. The resonance frequency estimates range from 0.5 to 3 Hz, as found from H/V. Taking H/V curve as input for retrieving subsurface information, we deploy diffuse field assumption (DFA) theory. The obtained shear wave velocity from the inversion of H/V curve through DFA approach provides evidence of the complex nature of the subsurface geological structures. Identifying six characteristic 2D cross-sections of the entire area, we attain prevalence of a low-velocity intermediate layer with velocity ranging from 128–192 m/s. On the contrary, a relatively high-velocity layer is also obtained (279–471 m/s) which can be treated as sedimentary deposits (may be for some sites as basin basement). The attained results, when extended to a 3D shear wave profile, tally excellently with estimated frequency distribution and its corresponding links with depth wise strata, accompanied by a topographical profile of the surveyed locations. All findings are comprehensively analyzed and interpreted as a proof of concept of implementation of DFA approach towards retrieving subsurface information.

3D S-wave velocity modelling with surface waves in oil seismic prospecting

It is a convenient and effective way to infer near-surface S-wave velocity () structures by using seismic surface waves. In spite of many successful applications on the geotechnical or engineering scale, surface-wave analysis and inversion methods are still not widely used in oil seismic exploration. Particularly, there are few researches reported on the three-dimensional (3D) structure modelling with the surface wave methods on this exploration scale. In this paper, we proposed a seismic surface wave data processing and inversion scheme for 3D near-surface modelling, and applied it to a field seismic data acquired for oil prospecting in Eastern China. Firstly, we analysed and adjusted the acquisition geometry to suit surface-wave analysis. Next, the interpolation and stacking processing was applied to the seismic data to eliminate spatial aliasing and improve the quality of dispersion images. In term of phase velocity dispersion imaging method, we adopted the cross-correlation and phase-shifting (CCPS) method to acquire accurate dispersion images. Simultaneous linearisation inversion of and layer thickness was used to inverse the surface wave dispersion curves. This inversion method reduces dependence of the initial models and has ability to detect the top interface of high-velocity layer. At last, the 3D near-surface structure was constructed by interpolating the all of 360 1D structures. We contrasted the surface wave inversion result with the first-arrival tomography inversion result, and the geological stratification results of both were coincident. Within the near-surface range, the surface wave inversion result has a higher resolution. This confirms that 3D modelling with surface waves in oil seismic prospecting is effective and practical.

Crustal and upper mantle structure beneath the South China Sea and Indonesia

AbstractA three-dimensional (3-D) S-velocity model for the crust and upper mantle beneath the South China Sea and Indonesia is presented, determined by means of Rayleigh wave analysis, in the depth range from 0 km to 400 km. The crustal and lithospheric mantle structure of this study area was previously investigated using several methods and databases. Due to their low resolution, a 3-D structure for this area has not been previously determined. The determination of such a 3-D S-velocity model is the goal of the present study. The most conspicuous features of the crust and upper mantle structure include the S-velocity difference between the Java Sea and the Banda Sea regions and a transitional boundary between these two regions. This model confirms the principal structural features revealed in previous studies: an oceanic crust structure in the center of the South China Sea, crustal thinning from the northern continental margin of the South China Sea to this oceanic crust, and the existence of a high-velocity layer in the lower crust of the northern continental margin. This study concludes that the north of the South China Sea is a nonvolcanic-type continental margin, solving the open question of whether the continental margin of the northern South China Sea is volcanic or nonvolcanic. A new map of the asthenosphere’s base is also presented.

MASW survey to estimate the unit weight of municipal solid waste at a landfill in Brazil

Non-invasive and non-destructive geophysical methods, such as the multichannel analysis of surface waves (MASW), can effectively provide useful information about the mechanical properties (stiffness and unit weight) of municipal solid waste (MSW), during and after landfill operation, for environmental monitoring and engineering analysis. This paper aims to address the results of a seismic survey performed at a sanitary landfill located 40 km north of Rio de Janeiro, Brazil, to image shear-wave velocity profiles to a depth of about 20 m. Seismic data were collected using the MASW method, performing an active and passive combined survey. Shear-wave velocities were used to compute the in situ unit weight distribution of MSW according to the empirical model proposed by Zekkos et al. Results indicated a two-layer model in which the bottom high-velocity layer is stiffer and denser than the top low-velocity layer. Despite the fact that the unit weight appeared to be underestimated for the upper low-velocity layer, model predictions may be graded qualitatively as excellent and potentially more accurate with well-calibrated parameters.

Joint inversion of Rayleigh and Love wave dispersion curves for improving the accuracy of near-surface S-wave velocities

High-frequency surface-wave techniques are extensively employed for the determination of S-wave velocities of near-surface materials. The absence of the measured phase velocity dispersion curves at specific frequency band, however, is common in the real world, which may cause inaccurate S-wave velocity by inversion. Additionally, surface-wave phase velocities are relatively insensitive to S-wave velocities under the abnormal high or low velocity layer, so it is difficult for surface-wave techniques to obtain S-wave velocities in irregular models which contain an (or several) abnormal layer(s). Based on significantly different sensitivity frequency bands of Rayleigh and Love wave phase velocities, a joint inversion method of Rayleigh and Love wave dispersion curves was proposed by the conjugate gradient algorithm. We used synthetic models to test the effectiveness of the developed method. Numerical modeling results revealed that: (1) S-wave velocities acquired by joint inversion of Rayleigh and Love wave phase velocities were more accurate than that by individual inversion in the case of lacking surface-wave dispersion data; (2) joint inversion efficiently improved the accuracy of S-wave velocities of irregular models. A real-world example verified the validity in application of the proposed approach.

High-Velocity Surface Layer Effects on Rayleigh Waves: Recommendations for Improved Shear-Wave Velocity Modeling

ABSTRACTSoil stiffness estimates are critical to geologic hazard and risk assessment in urban centers. Multichannel analysis of surface-wave (MASW) data collection along city streets is now a standard, cost-effective, and noninvasive soil stiffness approximation tool. With this approach, shear-wave velocities (VS) are derived from Rayleigh-wave signals. Although the current MASW practice is to neglect the effect of a high-velocity road layer on soil VS estimates, our models show measurable impacts on Rayleigh-wave amplitudes and phase velocities when seismic data are acquired on a road surface. Here, we compare synthetic models with field MASW and downhole VS measurements. Our modeling indicates that a road layer attenuates Rayleigh-wave signals across all frequencies, introduces coherent higher-mode signals, and leads to overestimated VS and VS30 values. We show that VS30 can be overestimated by more than 7% when soft soils underlie a rigid road surface. Inaccurate VS estimates can lead to improper soil classification and bias earthquake site-response estimates. For road-based MASW data analysis, we recommend incorporating a surface road layer in the Rayleigh-wave inversion to improve VS estimate accuracy with depth.

Problem of Using the PIV-Method for Measurements in Thin High-Velocity Shear Layers

Problem of Using the PIV-Method for Measurements in Thin High-Velocity Shear Layers

Full-waveform inversion of short-offset, band-limited seismic data in the Alboran Basin (SE Iberia)

Abstract. We present a high-resolution P-wave velocity model of the sedimentary cover and the uppermost basement to ∼3 km depth obtained by full-waveform inversion of multichannel seismic data acquired with a 6 km long streamer in the Alboran Sea (SE Iberia). The inherent non-linearity of the method, especially for short-offset, band-limited seismic data as this one, is circumvented by applying a data processing or modelling sequence consisting of three steps: (1) data re-datuming by back-propagation of the recorded seismograms to the seafloor; (2) joint refraction and reflection travel-time tomography combining the original and the re-datumed shot gathers; and (3) full-waveform inversion of the original shot gathers using the model obtained by travel-time tomography as initial reference. The final velocity model shows a number of geological structures that cannot be identified in the travel-time tomography models or easily interpreted from seismic reflection images alone. A sharp strong velocity contrast accurately defines the geometry of the top of the basement. Several low-velocity zones that may correspond to the abrupt velocity change across steeply dipping normal faults are observed at the flanks of the basin. A 200–300 m thick, high-velocity layer embedded within lower-velocity sediment may correspond to evaporites deposited during the Messinian crisis. The results confirm that the combination of data re-datuming and joint refraction and reflection travel-time inversion provides reference models that are accurate enough to apply full-waveform inversion to relatively short offset streamer data in deep-water settings starting at a field-data standard low-frequency content of 6 Hz.

Dynamics and wall collision of inertial particles in a solid–liquid turbulent channel flow

The dynamics and wall collision of inertial particles were investigated in non-isotropic turbulence of a horizontal liquid channel flow. The inertial particles were $125~\unicode[STIX]{x03BC}\text{m}$ glass beads at a volumetric concentration of 0.03 %. The bead-laden flow and the unladen base case had the same volumetric flow rates, with a shear Reynolds number, $Re_{\unicode[STIX]{x1D70F}}$, of the unladen flow equal to 410 based on the half-channel height and friction velocity. Lagrangian measurements of three-dimensional trajectories of both fluid tracers and glass beads were obtained using time-resolved particle tracking velocimetry based on the shake-the-box algorithm of Schanz et al. (Exp. Fluids, vol. 57, no. 5, 2016, pp. 1–27). The analysis showed that on average the near-wall glass beads decelerate in the streamwise direction, while farther away from the wall, the streamwise acceleration of the glass beads became positive. The ejection motions provided a local maximum streamwise acceleration above the buffer layer by transporting glass beads to high velocity layers and exposing them to a high drag force in the streamwise direction. Conversely, the sweep motion made the maximum contribution to the average streamwise deceleration of glass beads in the near-wall region. The wall-normal acceleration of the beads was positive in the vicinity of the wall, and it became negative farther from the wall. The investigation showed that the glass beads with sweeping motion had the maximum momentum, streamwise deceleration, and wall-normal acceleration among all the beads close to the wall and these values increased with increasing their trajectory angle. The investigation of the beads that collided with the wall showed that those with shallow impact angles (less than $1.5^{\circ }$) typically slide along the wall. The sliding beads had a small streamwise momentum exchange of ${\sim}5\,\%$ during these events. The duration of their sliding motion could be as much as five times the inner time scale of the unladen flow. The wall-normal velocity of these beads after sliding was greater than their wall-normal velocity before sliding, and was associated with the rotation induced lift force. Beads with impact angles greater than $1.5^{\circ }$ had shorter interaction times with the wall and smaller streamwise and wall-normal restitution ratios.

Low-velocity layers in the northwestern margin of the South China Sea: Evidence from receiver functions of ocean-bottom seismometer data

The receiver function method was applied to teleseismic recordings of an active-source ocean-bottom seismometer array in the northwestern margin of the South China Sea. Forward modeling of the receiver functions was used to derive velocity interfaces beneath the stations. Two main groups of low-velocity layers were imaged. The first group in the reef area, with a thickness of 7–10 km, exhibits a seaward uptrend of the buried depth but poor continuity. The second group, with a thickness of 3–4 km, is more continuous along the Zhongsha Trough; the buried depth decreases asymmetrically from the flanks to the rift center. A high shear wave velocity layer of ~4.0 km/s is imaged at the crust bottom beneath the Zhongsha Trough, with thickness of ~3 km. The average Vp/Vs in the Cenozoic sediment is 2.0–3.0 and was affected by high fluid activity induced by intensive faults. The Vp/Vs of the crust varies between 1.77 and 1.88, suggesting an intermediate to basic composition under the continental extension. Together, these results suggest a two-stage evolution model of the continental crust. In the first stage, the crust deformed in a ductile manner and thus created considerable shearing structures with high anisotropy that caused the obvious decrease of the shear wave velocity. In the second stage, the shearing structures connected asymmetrically, driven by detachment faults in the upper crust and upwelling of the lower crust. The Zhongsha Trough then formed, probably with magmatic underplating due to lithospheric extension or rising of hot mantle materials.

Mantle Structure in the Central Mediterranean Region From P and S Receiver Functions

AbstractWe investigate the upper mantle discontinuities in the central Mediterranean region by applying the P and S receiver function techniques on waveforms recorded at broadband stations located around the Tyrrhenian basin. P and S wave velocity profiles (down to 300‐km depth) are calculated with joint inversion of P and S receiver functions. We could identify the Moho, lithosphere‐asthenosphere boundary, and an underlying low‐velocity layer between ~60‐ and ~200‐km depth. The low‐velocity layer is interpreted as asthenospheric material, and its lower boundary is identified below the western Ionian and Tyrrhenian basins as a sharp Lehmann discontinuity. Although the stations are located on different lithospheric domains we find a strong correlation between Moho and the lithosphere‐asthenosphere boundary depths, which suggests ubiquitous coupling of the crust and lithospheric mantle, consistently with the southward opening of the Tyrrhenian basin. The Tyrrhenian and western Ionian basins present thinning of the transition zone of ~14 km, as inferred from a reduced P660s‐P410s differential time. Below the southern Apennines we observe a standard differential time that implies an average mantle transition zone thickness. We explain these mantle transition zone thickness variations as due to temperature heterogeneity linked to the area's subduction history. Finally, under central Europe (the location of the deep S‐to‐P conversion points) two strong signals from nonstandard discontinuities within the mantle transition zone are observed. These signals can be explained as being generated at the boundaries of high seismic velocity layers that are spatially correlated with stagnant slabs in the transition zone detected by seismic tomography.

Deep Crustal Faults, Shear Zones, and Magmatism in the Eastern Cordillera of Colombia: Growth of a Plateau From Teleseismic Receiver Function and Geochemical Mio‐Pliocene Volcanism Constraints

AbstractThe Eastern Cordillera of Colombia, in the northern Andes, is an example of an orogen in which Mesozoic basins were compressed during the Cenozoic, forming a ~2,500‐m‐high plateau in its northern portion. Significant shortening and crustal thickening have contributed to the construction of the present topography and elevation. In this contribution, we combine the use of teleseismic receiver functions, Hf isotopes, whole‐rock geochemistry, and U‐Pb dating to help elucidate the main mechanisms that played a role in the crustal thickening and uplift of the cordillera. Receiver functions calculated for three stations on top of the plateau are consistent with the presence of thrusts that converge into major crustal interfaces at upper‐middle crustal depths; they also suggest the existence of two crustal anisotropic layers beneath the western flank of the cordillera, which we interpret to have formed as a result of shearing. In the northern portion of the plateau, in the area where two Mio‐Pliocene volcanic domes and their related deposits outcrop, a lower crustal high seismic velocity layer is suggested by the receiver functions; we propose magmatic underplating for the origin of this layer. The geochemical characteristics of the volcanic rocks in the area are consistent with partial melt in a mantle influenced by slab‐related fluids; this magma could have been added to the crust and portions of it ascended and reached the surface, experiencing assimilation and differentiation during the process. We hypothesize that this Mio‐Pliocene volcanism was related to flattening of the Nazca subducting slab.

An experimental study of flow and heat transfer in a differentially side heated cavity filled with coarse porous media

Flow and heat transfer in a differentially side heated cubic cavity filled with relatively large solid spheres forming a coarse porous medium have been studied experimentally. Nusselt numbers were measured for Rayleigh numbers between 1.9 × 107 and 1.7 × 109, solid-to-fluid conductivity ratios between 0.32 and 618, and for different sphere sizes (d/H = 0.065, 0.14, 0.20), and packing geometries. The heat transfer results indicate that the presence of a porous medium in the cavity decreases the heat transfer compared to the pure-fluid cavity unless the solid spheres are highly conductive. We present a new Nusselt number correlation for coarse porous media based on porous medium dimensionless numbers. Particle image velocimetry and liquid crystal thermography measurements were performed in a refractive index-matched porous medium to obtain pore-scale velocity and temperature fields. The results show that the layers of spheres adjacent to the hot/cold walls play the most prominent role in the heat transfer reduction by hindering the formation of high-velocity boundary layers along the hot/cold walls, causing a portion of the boundary layer fluid to divert away from these walls, thus changing the stratified temperature distribution to a tilted one which leads to a lower overall heat transfer.

Redefining Dharwar Craton-Southern granulite terrain boundary in south India from new seismological constraints

The southern part of the Dharwar craton is an Archean granulite terrain that continues further south and joins with the Proterozoic Southern Granulite Terrain (SGT). The linkage and the boundary between the Dharwar craton and the SGT has been a subject of debate over the last 75 years. Based on adequate coverage of broadband seismological stations(80) over south India, we generated3-D shear velocity image of the crust through joint inversion of the P- receiver function and Rayleigh wave group velocity dispersions derived from the cross correlation of ambient noise time series analysis. The most significant finding is an unusually thick (15–28 km) high-velocity layer (HVL) with Vs > 4.0 km/sin the lowermost crust beneath the south Dharwar craton that continues southward in a most coherent fashion well beyond the southern limb of Palghat- Cauvery shear zone (PCSZ) widely considered to be the contact zone of the Dharwar and SGT. Elsewhere in south India the high-velocity layer is about 4–8 km thick similar to the global average. We interpret this HVL as a mafic magmatic underplate of Archean ancestry formed during granulite metamorphism. The study suggests that the Dharwar craton continues further south of the mapped orthopyroxene boundary to the Palghat shear zone in a continuous manner.

3D viscoelastic full waveform inversion of seismic waves for geotechnical site investigation

Full waveform inversion (FWI) methods are becoming efficient geophysical tools for geotechnical site investigation. They rely on a mathematical description of wave propagation phenomena to generate synthetic wave-fields, which are then matched with measured wave-fields for extraction of material properties. Due to the inherent computational challenges in implementing a viscoelastic treatment of the wave propagation phenomena, most of the existing 3D FWI algorithms are based on an elastic treatment, and hence ignore the anelastic behavior of materials. The focus of this study is to account for the anelastic effect of materials in the inversion analysis to improve inverted results. Therefore, a 3D viscoelastic FWI method is developed and tested on synthetic and field datasets. The method is based on an existing solution of 3D viscoelastic wave equations (finite-difference solver SOFI3D) and the adjoint-state inversion approach. The results show that the viscoelastic waveform analysis was able to characterize low- and high-velocity synthetic layers, and real variable soil layers. The S-wave velocity (Vs) profiles from field experiment generally agree with invasive standard penetration test (SPT) N-values, including identification of a low-velocity zone. Vs profiles obtained from a 3D elastic FWI are also included for comparison, and results from the viscoelastic inversion are more consistent with the SPT N-values in both trend and magnitudes.

AVO analysis of a shallow reverse polarity in Sydney Basin

A vast shallow reverse polarity which is extended across the PEP11 block in offshore Sydney basin and the lack of any wells in the area has wondered the interpreters about the mechanisms which has caused such a seismic signature in the area. This study aims to characterize this reverse polarity using the AVO analysis and pre stack inversion techniques in a pilot study. Baleen 2004 2-D towed streamer data are the only recent seismic data acquired in PEP11 block. Shallow depth water has left significant amount of multiple energy in shot records. The presence of a very high velocity sequence of layers which terminate at the shore line cause a strong ray bending letting small amount of the energy penetrate to deeper parts. The reverse polarity reflector is part of a sequence of progradational sediments which are accommodated at the top of the high velocity layer.

Rift structures and its related unconformities on and adjacent the Dongsha Rise: insights into the nature of the high-velocity layer in the northern South China Sea

It is curious that the typical feature of high-velocity layer (HVL) underneath the crust for the magma-rich margin was found in the magma-poor margin of the South China Sea. In order to better understand the nature and age of the HVL in the South China Sea, here we provide seismic imaging on the Cenozoic structure and sedimentation using a regional seismic reflection profile combined with existing drilling data and seismic refraction lines in the northeastern South China Sea. An important finding is that the extent of erosion since Neogene is only on the Dongsha Rise and is much smaller than that of the HVL observed across the northern margin of the South China Sea, which suggests the occurrence of the HVL has no influence on the erosion on Dongsha Rise through Neogene. On the regional seismic profiles, the different structures between the deepwater rifted margins and the continental shelf were also observed. The faults in the Zhuyi Sub-basins on the continental shelf are imaged to be high-angle and bound a series of grabens and horsts. In contrast, the deepwater region is characterized by tilted fault blocks and an array of listric normal faults, which extremely thinned the crust to be ~ 5–10 km. After middle Miocene, active magmatism occurred in the deepwater region at the time of post-spreading of oceanic crust. These listric faults on the hyper-extended crust is interpreted to be conduits for magma migration to the shallower levels. This typical structure in the deepwater region changed the geophysical nature of the HVL underneath the extreme thinned crust, which should be formed before the event of hyper-extension and is likely to be associated with the subduction of the paleo-Pacific toward the Asia in the late Cretaceous. Our study will answer the question why the South China Sea with the HVL underneath the crust is a magma-poor passive margin.