An analysis of the first-arrival times picked on the DSS and wide-angle seismic section recorded in Italy since 1968

We performed an analysis of refraction data recorded in Italy since 1968 in the frame of the numerous deep seismic sounding and wide-angle reflection/refraction projects. The aims of this study are to construct a parametric database including the recording geometric information relative to each profile, the phase pickings and the results of some kinematic analyses performed on the data, and to define a reference 1D velocity model for the Italian territory from all the available refraction data. As concerns the first goal, for each seismic section we picked the P-wave first-arrival-times, evaluated the uncertainties of the arrival-times pickings and determined from each travel time-offset curve the 1D velocity model. The study was performed on 419 seismic sections. Picking was carried out manually by an algorithm which includes the computation of three picking functions and the picking- error estimation. For each of the travel time-offset curves a 1D velocity model has been calculated. Actually, the 1D velocity-depth functions were estimated in three different ways which assume: a constant velocitygradient model, a varying velocity-gradient model and a layered model. As regards the second objective of this work, a mean 1D velocity model for the Italian crust was defined and compared with those used for earthquake hypocentre locations and seismic tomographic studies by different institutions operating in the Italian area, to assess the significance of the model obtained. This model can be used in future works as input for a next joint tomographic inversion of active and passive seismic data.

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Robust refraction statics solution and near-surface velocity model building using feedback from reflection data

Geophysics ◽

10.1190/geo2018-0060.1 ◽

2018 ◽

Vol 83 (6) ◽

pp. U63-U77

Author(s):

Bernard K. Law ◽

Daniel Trad

Keyword(s):

Model Building ◽

Waveform Inversion ◽

Velocity Model ◽

Surface Velocity ◽

Near Surface ◽

Arrival Times ◽

Reflection Data ◽

Velocity Model Building ◽

First Arrival ◽

Refraction Data

An accurate near-surface velocity model is critical for weathering statics correction and initial model building for depth migration and full-waveform inversion. However, near-surface models from refraction inversion often suffer from errors in refraction data, insufficient sampling, and over-simplified assumptions used in refraction algorithms. Errors in refraction data can be caused by picking errors resulting from surface noise, attenuation, and dispersion of the first-arrival energy with offset. These errors are partially compensated later in the data flow by reflection residual statics. Therefore, surface-consistent residual statics contain information that can be used to improve the near-surface velocity model. We have developed a new dataflow to automatically include median and long-wavelength components of surface-consistent reflection residual statics. This technique can work with any model-based refraction solution, including grid-based tomography methods and layer-based methods. We modify the cost function of the refraction inversion by adding model and data weights computed from the smoothed surface-consistent residual statics. By using an iterative inversion, these weights allow us to update the near-surface velocity model and to reject first-arrival picks that do not fit the updated model. In this nonlinear optimization workflow, the refraction model is derived from maximizing the coherence of the reflection energy and minimizing the misfit between model arrival times and the recorded first-arrival times. This approach can alleviate inherent limitations in shallow refraction data by using coherent reflection data.

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Passive seismic tomography using recorded microseismicity: Application to mining-induced seismicity

Geophysics ◽

10.1190/geo2018-0076.1 ◽

2019 ◽

Vol 84 (1) ◽

pp. B41-B57 ◽

Cited By ~ 4

Author(s):

Himanshu Barthwal ◽

Mirko van der Baan

Keyword(s):

Seismic Tomography ◽

Velocity Model ◽

P Wave ◽

Double Difference ◽

Lateral Velocity ◽

Study Region ◽

Arrival Times ◽

3D Velocity Model ◽

Passive Seismic ◽

Dip Angle

Microseismicity is recorded during an underground mine development by a network of seven boreholes. After an initial preprocessing, 488 events are identified with a minimum of 12 P-wave arrival-time picks per event. We have developed a three-step approach for P-wave passive seismic tomography: (1) a probabilistic grid search algorithm for locating the events, (2) joint inversion for a 1D velocity model and event locations using absolute arrival times, and (3) double-difference tomography using reliable differential arrival times obtained from waveform crosscorrelation. The originally diffusive microseismic-event cloud tightens after tomography between depths of 0.45 and 0.5 km toward the center of the tunnel network. The geometry of the event clusters suggests occurrence on a planar geologic fault. The best-fitting plane has a strike of 164.7° north and dip angle of 55.0° toward the west. The study region has known faults striking in the north-northwest–south-southeast direction with a dip angle of 60°, but the relocated event clusters do not fall along any mapped fault. Based on the cluster geometry and the waveform similarity, we hypothesize that the microseismic events occur due to slips along an unmapped fault facilitated by the mining activity. The 3D velocity model we obtained from double-difference tomography indicates lateral velocity contrasts between depths of 0.4 and 0.5 km. We interpret the lateral velocity contrasts in terms of the altered rock types due to ore deposition. The known geotechnical zones in the mine indicate a good correlation with the inverted velocities. Thus, we conclude that passive seismic tomography using microseismic data could provide information beyond the excavation damaged zones and can act as an effective tool to complement geotechnical evaluations.

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RefPick: A GUI Application to Pick First Arrival Times and Data Processing on Seismic Refraction Data

8th Congress of the Balkan Geophysical Society ◽

10.3997/2214-4609.201414209 ◽

2015 ◽

Author(s):

K.H. Coban ◽

M. Senkaya ◽

H. Karslı

Keyword(s):

Data Processing ◽

Seismic Refraction ◽

Arrival Times ◽

First Arrival ◽

Seismic Refraction Data ◽

Refraction Data

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Imaging of the Upper Mantle Beneath Southeast Asia: Constrained by Teleseismic P-Wave Tomography

Remote Sensing ◽

10.3390/rs12182975 ◽

2020 ◽

Vol 12 (18) ◽

pp. 2975

Author(s):

Huiyan Shi ◽

Tonglin Li ◽

Rongzhe Zhang ◽

Gongcheng Zhang ◽

Hetian Yang

Keyword(s):

South China Sea ◽

Southeast Asia ◽

Travel Time ◽

South China ◽

High Velocity ◽

Velocity Model ◽

P Wave ◽

Deep Part ◽

Low Velocity ◽

Velocity Anomalies

It is of great significance to construct a three-dimensional underground velocity model for the study of geodynamics and tectonic evolution. Southeast Asia has attracted much attention due to its complex structural features. In this paper, we collected relative travel time residuals data for 394 stations distributed in Southeast Asia from 2006 to 2019, and 14,011 seismic events were obtained. Then, teleseismic tomography was applied by using relative travel time residuals data to invert the velocity where the fast marching method (FMM) and subspace method were used for every iteration. A novel 3D P-wave velocity model beneath Southeast Asia down to 720 km was obtained using this approach. The tomographic results suggest that the southeastern Tibetan Plateau, the Philippines, Sumatra, and Java, and the deep part of Borneo exhibit high velocity anomalies, while low velocity anomalies were found in the deep part of the South China Sea (SCS) basin and in the shallow part of Borneo and areas near the subduction zone. High velocity anomalies can be correlated to subduction plates and stable land masses, while low velocity anomalies can be correlated to island arcs and upwelling of mantle material caused by subduction plates. We found a southward subducting high velocity body in the Nansha Trough, which was presumed to be a remnant of the subduction of the Dangerous Grounds into Borneo. It is further inferred that the Nansha Trough and the Dangerous Grounds belong to the same tectonic unit. According to the tomographic images, a high velocity body is located in the deep underground of Indochina–Natuna Island–Borneo–Palawan, depth range from 240 km to 660 km. The location of the high velocity body is consistent with the distribution range of the ophiolite belt, so we speculate that the high velocity body is the remnant of thee Proto-South China Sea (PSCS) and Paleo-Tethys. This paper conjectures that the PSCS was the southern branch of Paleo-Tethys and the gateway between Paleo-Tethys and the Paleo-Pacific Ocean. Due to the squeeze of the Australian plate, PSCS closed from west to east in a scissor style, and was eventually extinct under Borneo.

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Joint microseismic event location and anisotropic velocity inversion with the cross double-difference method using downhole microseismic data

Geophysics ◽

10.1190/geo2019-0325.1 ◽

2020 ◽

Vol 85 (3) ◽

pp. KS63-KS73

Author(s):

Yangyang Ma ◽

Congcong Yuan ◽

Jie Zhang

Keyword(s):

Arrival Time ◽

Velocity Model ◽

P Wave ◽

Double Difference ◽

S Wave ◽

Arrival Times ◽

Monitoring Well ◽

The Cross ◽

Microseismic Event ◽

Wave Arrival

We have applied the cross double-difference (CDD) method to simultaneously determine the microseismic event locations and five Thomsen parameters in vertically layered transversely isotropic media using data from a single vertical monitoring well. Different from the double-difference (DD) method, the CDD method uses the cross-traveltime difference between the S-wave arrival time of one event and the P-wave arrival time of another event. The CDD method can improve the accuracy of the absolute locations and maintain the accuracy of the relative locations because it contains more absolute information than the DD method. We calculate the arrival times of the qP, qSV, and SH waves with a horizontal slowness shooting algorithm. The sensitivities of the arrival times with respect to the five Thomsen parameters are derived using the slowness components. The derivations are analytical, without any weak anisotropic approximation. The input data include the cross-differential traveltimes and absolute arrival times, providing better constraints on the anisotropic parameters and event locations. The synthetic example indicates that the method can produce better event locations and anisotropic velocity model. We apply this method to the field data set acquired from a single vertical monitoring well during a hydraulic fracturing process. We further validate the anisotropic velocity model and microseismic event locations by comparing the modeled and observed waveforms. The observed S-wave splitting also supports the inverted anisotropic results.

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Full waveform inversion of short-offset, band-limited seismic data inthe Alboran basin (SE Iberia)

10.5194/se-2019-46 ◽

2019 ◽

Author(s):

Clàudia Gras ◽

Valentí Sallarès ◽

Daniel Dagnino ◽

C. Estela Jiménez ◽

Adrià Meléndez ◽

...

Keyword(s):

Travel Time ◽

Seismic Data ◽

Waveform Inversion ◽

Velocity Model ◽

P Wave ◽

Full Waveform Inversion ◽

Time Inversion ◽

Full Waveform ◽

Travel Time Tomography ◽

Band Limited

Abstract. We present a high-resolution P-wave velocity model of the sedimentary cover and the uppermost basement until ~ 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/modeling 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) FWI 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 field-data standard low frequency content of 6 Hz.

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TTZ-SOUTH seismic experiment

Geofizicheskiy Zhurnal ◽

10.24028/gzh.v43i2.230189 ◽

2021 ◽

Vol 43 (2) ◽

pp. 28-44

Author(s):

T. Janik ◽

V. Starostenko ◽

P. Aleksandrowski ◽

T. Yegorova ◽

W. Czuba ◽

...

Keyword(s):

High Velocity ◽

Velocity Model ◽

Data Cube ◽

P Wave ◽

Depth Range ◽

Time Inversion ◽

Crust And Upper Mantle ◽

Moho Interface ◽

East European ◽

First Arrival

The wide-angle reflection and refraction (WARR) TTZ-South transect carried out in 2018 crosses the SW region of Ukraine and the SE region of Poland. The TTZ-South profile targeted the structure of the Earth’s crust and upper mantle of the Trans-European Suture Zone, as well as the southwestern segment of the East European Craton (slope of the Ukrainian Shield). The ~550 km long profile (~230 km in Poland and ~320 km in western Ukraine) is an extension of previously realized projects in Poland, TTZ (1993) and CEL03 (2000). The deep seismic sounding study along the TTZ-South profile using TEXAN and DATA-CUBE seismic stations (320 units) made it possible to obtain high-quality seismic records from eleven shot points (six in Ukraine and five in Poland). This paper presents a smooth P wave velocity model based on first-arrival travel-time inversion using the FAST (First Arrival Seismic Tomography) code. The obtained image represents a preliminary velocity model which, according to the P wave velocities, consists of a sedimentary layer and the crystalline crust that could comprise upper, middle and lower crustal layers. The Moho interface, approximated by the 7.5 km/s isoline, is located at 45—47 km depth in the central part of the profile, shallowing to 40 and 37 km depth in the northern (Radom-Łysogуry Unit, Poland) and southern (Volyno-Podolian Monocline, Ukraine) segments of the profile, respectively. A peculiar feature of the velocity cross-section is a number of high-velocity bodies distinguished in the depth range of 10—35 km. Such high-velocity bodies were detected previously in the crust of the Radom-Łysogуry Unit. These bodies, inferred at depths of 10—35 km, could be allochthonous fragments of what was originally a single mafic body or separate mafic bodies intruded into the crust during the break-up of Rodinia in the Neoproterozoic, which was accompanied by considerable rifting. The manifestations of such magmatism are known in the NE part of the Volyno-Podolian Monocline, where the Vendian trap formation occurs at the surface.

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Three-dimensional crustal Vp and Vs structures beneath the southern segment of the Tan-Lu fault revealed by active source and earthquake data

Geophysical Journal International ◽

10.1093/gji/ggaa314 ◽

2020 ◽

Vol 223 (3) ◽

pp. 2148-2165

Author(s):

Yunpeng Zhang ◽

Baoshan Wang ◽

Tao Xu ◽

Wei Yang ◽

Weitao Wang ◽

...

Keyword(s):

Crustal Structure ◽

Yangtze River ◽

Velocity Structure ◽

Eastern China ◽

P Wave ◽

Arrival Times ◽

Local Earthquakes ◽

Active Source ◽

First Arrival ◽

Earthquake Data

SUMMARY The 2400-km-long Tan-Lu fault, the largest deformation zone in eastern China, plays a decisive role in the seismicity, regional tectonics and mineral deposits distributions. However, the velocity structure beneath the Tan-Lu fault, particularly in the southern segment, is poorly imaged due to the lack of local earthquakes. To obtain a high-resolution crustal structure image, we carried out an active source experiment by firing mobile airgun sources along the Yangtze River in the Anhui Province in October 2015. We manually picked 4118 P wave and 1906 Swave first arrival times from the airgun signals. We also collected 28 957 P wave and 26 257 S wave first arrival times from local earthquakes in a larger area. 3-D crustal velocity images beneath the southern segment of the Tan-Lu fault and surrounding areas are studied using traveltime tomography. Compared with the local earthquake data, the active source data provide better constraints on the upper crustal structure, which further refines the resolution of the lower-crust structure. The Vp and Vs crustal structures are consistent with the local geological settings, and earthquakes are primarily clustered near faults and are spatially correlated with low-velocity zones. Strong velocity contrasts are observed across the Tan-Lu fault zone, which is the main factor controlling local anomalies. The high Vp, Vs and Vp/Vs beneath the Qinling-Dabie orogenic belt and the Middle-Lower Yangtze River Metallogenic Belt may relate to Mesozoic lithospheric delamination and asthenospheric upwelling. These results also demonstrate that the mobile large-volume airgun sources are promising tools for 3-D crustal structure surveys.

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