Shallow Seismic Reflection Investigation of Unstable Sedimentary Deposits
                        in the Dăneasa Area, Romania

Results of shallow seismic reflection measurements, performed over an area with unstable sedimentary formations in the near subsurface, are presented. The investigated area is located on the Olt Valley, in the vicinity of the Dăneasa village, Romania, crossed by a railway line and a national road on which the traffic is very intense. Data were collected along a linear profile, with a length of 94 m, perpendicular to the railway line and the national road using a fixed spread of 48 vertical-component geophones with the sources rolling along the acquisition line. The surface waves generated by the intense traffic on the national road interfered with the seismic arrivals seen on most of shot gathers, especially with those seen on the traces from receiver locations greater than 48 m. The interrupted continuity of two shallow reflectors, R1 and R2, seen on the depth-converted seismic section at depth values shallower than 30 m, could be interpreted as an effect of the presence of two steep failure planes deveIoped into the ground. A P-wave velocity-depth model down to a depth of 20 m after first-arrival traveltime tomography was then created, on which four sedimentary layers with variable thicknesses and constant velocities, separated by the interfaces L1, L2 and L3, were interpreted. By comparing the depth-converted seismic section with the P-wave velocity-depth model, the reflectors R1 and R2 on the seismic section correspond pretty well with the interfaces L2 and L3 from the velocity-depth model.

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Iterative P-wave velocity inversion using Markov chain Monte Carlo method

10.5194/egusphere-egu2020-6298 ◽

2020 ◽

Author(s):

Hyunggu Jun ◽

Hyeong-Tae Jou ◽

Han-Joon Kim ◽

Sang Hoon Lee

Keyword(s):

Wave Velocity ◽

Seismic Data ◽

Velocity Structure ◽

Low Frequency ◽

P Wave ◽

Velocity Analysis ◽

Seismic Section ◽

Traveltime Tomography ◽

P Wave Velocity ◽

Frequency Components

Imaging the subsurface structure through seismic data needs various information and one of the most important information is the subsurface P-wave velocity. The P-wave velocity structure mainly influences on the location of the reflectors during the subsurface imaging, thus many algorithms has been developed to invert the accurate P-wave velocity such as conventional velocity analysis, traveltime tomography, migration velocity analysis (MVA) and full waveform inversion (FWI). Among those methods, conventional velocity analysis and MVA can be widely applied to the seismic data but generate the velocity with low resolution. On the other hands, the traveltime tomography and FWI can invert relatively accurate velocity structure, but they essentially need long offset seismic data containing sufficiently low frequency components. Recently, the stochastic method such as Markov chain Monte Carlo (McMC) inversion was applied to invert the accurate P-wave velocity with the seismic data without long offset or low frequency components. This method uses global optimization instead of local optimization and poststack seismic data instead of prestack seismic data. Therefore, it can avoid the problem of the local minima and limitation of the offset. However, the accuracy of the poststack seismic section directly affects the McMC inversion result. In this study, we tried to overcome the dependency of the McMC inversion on the poststack seismic section and iterative workflow was applied to the McMC inversion to invert the accurate P-wave velocity from the simple background velocity and inaccurate poststack seismic section. The numerical test showed that the suggested method could successfully invert the subsurface P-wave velocity.

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Metode Seismik dalam Pemodelan Fisis Letusan Gunung Lumpur Bledug Kuwu

JURNAL PENDIDIKAN TEKNOLOGI KEJURUAN ◽

10.24036/jptk.v2i2.19423 ◽

2019 ◽

Vol 2 (2) ◽

pp. 61-66

Author(s):

Ahmad Fauzi Pohan ◽

Rusnoviandi Rusnoviandi

Keyword(s):

Wave Velocity ◽

Physical Modeling ◽

Vertical Component ◽

Dominant Frequency ◽

P Wave ◽

Physical Parameters ◽

S Wave ◽

Interesting Phenomenon ◽

Central Java ◽

P Wave Velocity

Aktivitas gunung lumpur Bledug Kuwu di Jawa Tengah merupakan fenomena yang menarik dikaji menggunakan pemodelan fisis. Tujuan penelitian ini adalah mengetahui parameter dari medium gunung lumpur Bledug Kuwu. Adapun pemodelan fisis yang dilakukan dengan menggunakan media fisis akuarium berukuran 59 × 59 × 37,3 cm yang diisi material dari lumpur Bledug Kuwu. Sumber letusan dihasilkan dari tekanan kompresor yang dapat diatur kedalaman (10.5, 13, dan 15.5 cm) dan sudut (30o, 45o dan 60o) sumbernya. Sensor yang digunakan geophone komponen vertikal sebanyak 3 buah dengan durasi perekaman selama 5 dan 2,5 detik. Data diambil dengan frekuensi sampel 2 dan 4 kHz untuk masing-masing durasi perekaman. Konfigurasi sumber dan geophone dibuat sesuai dengan pemodelan fisisnya. Pengukuran desnsitas lumpur menunjukkan angka sebesar 1200 kg/m3. Berdasarkan hasil analisis seismogram model fisis diperoleh kecepatan perambatan gelombang-P pada medium lumpur Bledug Kuwu adalah sebesar 48,74 m/s,dan gelombang-S sebesar 28,14 m/s dengan frekuensi dominan antara 20 sampai 25 Hz. Bledug Kuwu mud volcano activity in Central Java is an interesting phenomenon to be studied using both physical modeling. The objective of this study was to determine the physical parameters of the medium of Bledug Kuwu. The Physical model was an aquarium with a dimension of 59 × 59 × 37.3 cm filled with Bledug Kuwu’s mud. The eruption source is generated by a compressor pressure that can be controled both the depth(10.5, 13, and 15.5 cm) and the angel of the source (30o, 45o and 60o). The resulting seismic signals were recorded by using 3 vertical component geophones for 10 and 5 seconds durations at a frequency of 2 and 4 kHz respectivel, mud density 1200 kg/m3 . The physical modeling shows that the P-wave velocity of the Bledug Kuwu’s medium is 48.7 m/s, S-wave velocity of Bledug Kuwu’s is 28,14 m/s with a dominant frequency of 20 to 25 Hz.

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Lithospheric structure of the Iberian Central System (Iberian Massif) imaged by the wide-angle seismic reflection/refraction CIMDEF experiment

10.5194/egusphere-egu21-2739 ◽

2021 ◽

Author(s):

Irene DeFelipe ◽

Puy Ayarza ◽

Imma Palomeras ◽

Juvenal Andrés ◽

Mario Ruiz ◽

...

Keyword(s):

Wave Velocity ◽

Seismic Reflection ◽

P Wave ◽

Lithospheric Structure ◽

Mountain Range ◽

Wide Angle ◽

Topographic Feature ◽

Iberian Massif ◽

Central System ◽

P Wave Velocity

The Iberian Central System represents an outstanding topographic feature in the central Iberian Peninsula. It is an intraplate mountain range formed by igneous and metasedimentary rocks of the Variscan Iberian Massif that has been exhumed since the Eocene in the context of the Alpine orogeny. The Iberian Central System has been conventionally interpreted as a thick-skinned pop-up mountain range thrust over the Duero and Tajo foreland basins. However, its lithospheric structure and the P-wave velocity distribution are not yet fully resolved. In order to place geophysical constraints on this relevant topographic feature, to identify lithospheric discontinuities, and to unravel the crustal deformation mechanisms, a wide-angle seismic reflection and refraction experiment, CIMDEF (Central Iberian Mechanism of DEFormation), was acquired in 2017 and 2019. It is a NNW-SSE oriented 360-km long profile that runs through the Duero basin, the Iberian Central System and the Tajo basin. First results based on forward modeling by raytracing show an irregularly layered lithosphere and allow to infer the depth extent of the northern Iberian Central System batholith. The crust is ~ 31 km thick under the Duero and Tajo basins and thickens to ~ 39 km under the Iberian Central System. A conspicuous thinning of the lower crust towards the south of the Iberian Central System is also modeled. Along this transect, a continuous and high amplitude upper mantle feature is observed and modeled as the reflection of an interface dipping from 58 to 62 km depth featuring a P-wave velocity contrast of 8.2 to 8.3 km/s. Our preliminary results complement previous models based on global-phase seismic and noise interferometry and gravity data, provide new constraints to validate the accuracy of passive seismic methods at lithospheric scale, and contribute with a resolute P-wave velocity model of the study area to unravel the effect of the Alpine reactivation on the central Iberian Massif. This project has been funded by the EIT-RawMaterials 17024 (SIT4ME) and the MINECO projects: CGL2016-81964-REDE, CGL2014-56548-P.

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Physical Properties and Structure of the Near Subsurface in the Săcel Area, Romania, from Shallow Seismic Measurements

Journal of Environmental and Engineering Geophysics ◽

10.2113/jeeg24.1.151 ◽

2019 ◽

Vol 24 (1) ◽

pp. 151-158

Author(s):

Ionelia Panea

Keyword(s):

Wave Velocity ◽

Signal To Noise Ratio ◽

Soil Surface ◽

Geological Structure ◽

P Wave ◽

S Wave ◽

Sedimentary Deposits ◽

Shallow Seismic ◽

P Wave Velocity ◽

Good Signal

Results are presented for shallow seismic reflection measurements performed southwest of Săcel village in Romania for the purpose of obtaining information about the geological structure in the near subsurface. The P-wave and S-wave velocity distributions were also obtained below the soil surface. The measurements were performed along a nearly linear profile on the top of an elongated hill. Most of the shot gathers were characterized by a good signal-to-noise ratio. A depth-converted migrated section was obtained after the processing of shot gathers, on which an image of sedimentary deposits with various thicknesses, separated by shallow faults until a depth of about 80 m, were observed. The P-wave and S-wave velocity-depth models for two segments were of considerable interest for a geotechnical study proposed for the construction of a windmill park. The two- and three-layered P-wave velocity-depth models were comparable until depths of about 10 m after first-arrival traveltime inversions. The lateral variations in the subsurface geological structure and lithology reflected the variations in the P-wave velocity values from both models. The S-wave velocity-depth models for comparable depth intervals were similar to those from the P-wave velocity-depth models. Reliable S-wave velocity distributions were obtained after inversion of fundamental-mode and higher-mode surface waves.

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Time–frequency windowing in multiparameter elastic FWI of shallow seismic wavefield

Geophysical Journal International ◽

10.1093/gji/ggaa242 ◽

2020 ◽

Vol 222 (2) ◽

pp. 1164-1177

Author(s):

Nikolaos Athanasopoulos ◽

Edgar Manukyan ◽

Thomas Bohlen ◽

Hansruedi Maurer

Keyword(s):

Wave Velocity ◽

Time Window ◽

Mass Density ◽

Waveform Inversion ◽

P Wave ◽

S Wave ◽

Time Frequency ◽

Full Waveform ◽

Shallow Seismic ◽

P Wave Velocity

SUMMARY Full-waveform inversion of shallow seismic wavefields is a promising method to infer multiparameter models of elastic material properties (S-wave velocity, P-wave velocity and mass density) of the shallow subsurface with high resolution. Previous studies used either the refracted Pwaves to reconstructed models of P-wave velocity or the high-amplitude Rayleigh waves to infer the S-wave velocity structure. In this work, we propose a combination of both wavefields using continuous time–frequency windowing. We start with the contribution of refracted P waves and gradually increase the time window to account for scattered body waves, higher mode Rayleigh waves and finally the fundamental Rayleigh wave mode. The opening of the time window is combined with opening the frequency bandwidth of input signals to avoid cycle skipping. Synthetic reconstruction tests revealed that the reconstruction of P-wave velocity model and mass density can be improved. The S-wave velocity reconstruction is still accurate and robust and is slightly benefitted by time–frequency windowing. In a field data application, we observed that time–frequency windowing improves the consistency of multiparameter models. The inferred models are in good agreement with independent geophysical information obtained from ground-penetrating radar and full-waveform inversion of SH waves.

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3D P-wave velocity image beneath the Pannonian Basin using traveltime tomography

Acta Geodaetica et Geophysica ◽

10.1007/s40328-019-00267-3 ◽

2019 ◽

Vol 54 (3) ◽

pp. 373-386 ◽

Cited By ~ 1

Author(s):

Máté Timkó ◽

István Kovács ◽

Zoltán Wéber

Keyword(s):

Wave Velocity ◽

Pannonian Basin ◽

P Wave ◽

Traveltime Tomography ◽

P Wave Velocity ◽

Velocity Image

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CHARACTERISTICS OF P-WAVE VELOCITY AND SEISMIC REFLECTION OF THE SEDIMENTARY LAYER IN THE SOUTH YELLOW SEA

Marine Geology & Quaternary Geology ◽

10.3724/sp.j.1140.2011.02073 ◽

2011 ◽

Vol 31 (2) ◽

pp. 73-78 ◽

Cited By ~ 2

Author(s):

Zhiqiang WU ◽

Kai LU

Keyword(s):

Wave Velocity ◽

Yellow Sea ◽

Seismic Reflection ◽

P Wave ◽

South Yellow Sea ◽

The South ◽

P Wave Velocity ◽

The South Yellow Sea ◽

Sedimentary Layer

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A new 3-D P-wave velocity model for the Gulf of Cadiz and adjacent areas derived from controlled-source seismic data: application to nonlinear probabilistic relocation of moderate earthquakes

Geophysical Journal International ◽

10.1093/gji/ggz562 ◽

2019 ◽

Vol 221 (1) ◽

pp. 1-19

Author(s):

Lucía Lozano ◽

Juan Vicente Cantavella ◽

Jaime Barco

Keyword(s):

Wave Velocity ◽

Seismic Reflection ◽

Velocity Model ◽

P Wave ◽

Gulf Of Cadiz ◽

Uppermost Mantle ◽

Controlled Source ◽

Reflection And Refraction ◽

P Wave Velocity ◽

Gulf Of Cádiz

SUMMARY The SW Iberian margin is well known for its complex tectonic setting and crustal structure and by the occurrence of moderate magnitude earthquakes and some great tsunamigenic earthquakes. Fortunately, many seismic reflection and refraction profiles have been carried out, providing detailed information about the crustal structure of the main geologic domains in this region. These studies show a first-order variation due to the transition from oceanic to continental domain, large-scale heterogeneities within the crust and an irregular Moho topography. Routine earthquake locations in this area have been usually computed using a general 1-D velocity model which is clear that cannot account for such a heterogeneous structure. In addition, regional seismic stations used to locate the Gulf of Cadiz seismicity are on land and far away to the east, implying large azimuthal gaps and distances. In this context, a 3-D approach seems necessary to properly solve the crustal velocity field and improve earthquake location in this area. With this purpose, we present a new digital 3-D P-wave velocity distribution for the crust and uppermost mantle derived from previously published controlled-source seismic experiments carried out in SW Iberia and the Gulf of Cadiz over the last 40 yr. We have reviewed more than 50 wide-angle and multichannel seismic reflection and refraction profiles and digitized the most significant published 2-D seismic velocity models, performing an updated compilation of crustal parameters (P-wave velocities and geometry and depth of the main crustal interfaces). These velocities as a function of position and depth have been interpolated using ordinary kriging algorithm to obtain, in the form of a regular georeferenced 20 × 20 × 1 km grid spacing, a high-resolution 3-D P-wave velocity distribution for the crust and uppermost mantle and a continuous Moho depth map of the whole area of this study (33°N–41°N latitude and 15°W–5°W longitude). Since current seismic location tools allow the implementation of 3-D grid structures, we have applied our 3-D model to relocate a selection of moderate earthquakes occurred in the studied region using a probabilistic nonlinear method. In the Gulf of Cadiz area the probabilistic approximation provides maximum likelihood hypocentres located within the uppermost mantle with the majority of depths ranging between 20 and 45 km. This model would subsequently be implemented at the Spanish Seismic Network for the routine relocation of the seismicity of the area.

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High‐resolution crosswell imaging of a west Texas carbonate reservoir: Part 5—Core analysis

Geophysics ◽

10.1190/1.1443810 ◽

1995 ◽

Vol 60 (3) ◽

pp. 712-726 ◽

Cited By ~ 13

Author(s):

Richard C. Nolen‐Hoeksema ◽

Zhijing Wang ◽

Jerry M. Harris ◽

Robert T. Langan

Keyword(s):

Wave Velocity ◽

Field Experiments ◽

Velocity Ratio ◽

Carbonate Reservoir ◽

P Wave ◽

Core Analysis ◽

S Wave ◽

Traveltime Tomography ◽

West Texas ◽

P Wave Velocity

We conducted a core analysis program to provide supporting data to a series of crosswell field experiments being carried out in McElroy Field by Stanford University’s Seismic Tomography Project. The objective of these experiments is to demonstrate the use of crosswell seismic profiling for reservoir characterization and for monitoring [Formula: see text] flooding. For these west Texas carbonates, we estimate that [Formula: see text] saturation causes P‐wave velocity to change by −1.9% (pooled average, range = −6.3 to +0.1%), S‐wave velocity by +0.6% (range = 0 to 2.7%), and the P‐to‐S velocity ratio by −2.4% (range = −6.4 to −0.3%). When we compare these results to the precisions we can expect from traveltime tomography (about ±1% for P‐ and S‐wave velocity and about ±2% for the P‐to‐S velocity ratio), we conclude that time‐lapse traveltime tomography is sensitive enough to resolve changes in the P‐wave velocity, S‐wave velocity, and P‐to‐S velocity ratio that result from [Formula: see text] saturation. We concentrated here on the potential for [Formula: see text] saturation to affect seismic velocities. The potential for [Formula: see text] saturation to affect other seismic properties, not discussed here, may prove to be more significant (e.g., P‐wave and S‐wave impedance).

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