Lithospheric architecture of the Ligurian Basin from seismic travel time tomography

The Ligurian Basin is located north-west of Corsica at the transition from the western Alpine orogen to the Apennine system. The Back-arc basin was generated by the southeast retreat of the Apennines-Calabrian subduction zone. The opening took place from late Oligocene to Miocene. While the extension led to extreme continental thinning little is known about the style of back-arc rifting. Today, seismicity indicates the closure of this back-arc basin. In the basin, earthquake clusters occur in the lower crust and uppermost mantle and are related to re-activated, inverted, normal faults created during rifting.To shed light on the present day crustal and lithospheric architecture of the Ligurian Basin, active seismic data have been recorded on short period ocean bottom seismometers in the framework of SPP2017 4D-MB, the German component of AlpArray. An amphibious refraction seismic profile was shot across the Ligurian Basin in an E-W direction from the Gulf of Lion to Corsica. The profile comprises 35 OBS and three land stations at Corsica to give a complete image of the continental thinning including the necking zone.The majority of the refraction seismic data show mantle phases with offsets up to 70 km. The arrivals of seismic phases were picked and used to generate a 2-D P-wave velocity model. The results show a crust-mantle boundary in the central basin at ~12 km depth below sea surface. The P-wave velocities in the crust reach 6.6 km/s at the base. The uppermost mantle shows velocities >7.8 km/s. The crust-mantle boundary becomes shallower from ~18 km to ~12 km depth within 30 km from Corsica towards the basin centre. The velocity model does not reveal an axial valley as expected for oceanic spreading. Further, it is difficult to interpret the seismic data whether the continental lithosphere was thinned until the mantle was exposed to the seafloor. However, an extremely thinned continental crust indicates a long lasting rifting process that possibly did not initiate oceanic spreading before the opening of the Ligurian Basin stopped. The distribution of earthquakes and their fault plane solutions, projected along our seismic velocity model, is in-line with the counter-clockwise opening of the Ligurian Basin.

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Investigations of the Oligocene-Miocene opening of the Ligurian Basin using refraction seismic data

10.5194/egusphere-egu2020-6950 ◽

2020 ◽

Author(s):

Heidrun Kopp ◽

Anke Dannowski ◽

Ingo Grevemeyer ◽

Dietrich Lange ◽

Martin Thorwart ◽

...

Keyword(s):

Seismic Data ◽

Central Basin ◽

Ocean Bottom ◽

North West ◽

Mantle Boundary ◽

Oceanic Spreading ◽

Refraction Seismic ◽

Short Period ◽

Back Arc ◽

Ligurian Basin

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Reconnaissance seismic refraction-reflection surveys in northwestern New Mexico

Bulletin of the Seismological Society of America ◽

10.1785/bssa0740041263 ◽

1984 ◽

Vol 74 (4) ◽

pp. 1263-1274

Author(s):

Lawrence H. Jaksha ◽

David H. Evans

Keyword(s):

New Mexico ◽

Wave Velocity ◽

Lower Crust ◽

Seismic Waves ◽

Seismic Refraction ◽

Velocity Model ◽

P Wave ◽

Uppermost Mantle ◽

P Wave Velocity ◽

Crustal Thinning

Abstract A velocity model of the crust in northwestern New Mexico has been constructed from an interpretation of direct, refracted, and reflected seismic waves. The model suggests a sedimentary section about 3 km thick with an average P-wave velocity of 3.6 km/sec. The crystalline upper crust is 28 km thick and has a P-wave velocity of 6.1 km/sec. The lower crust below the Conrad discontinuity has an average P-wave velocity of about 7.0 km/sec and a thickness near 17 km. Some evidence suggests that velocity in both the upper and lower crust increases with depth. The P-wave velocity in the uppermost mantle is 7.95 ± 0.15 km/sec. The total crustal thickness near Farmington, New Mexico, is about 48 km (datum = 1.6 km above sea level), and there is evidence for crustal thinning to the southeast.

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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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Anisotropy extraction using a deviated well in the Mahanadi Basin, East Coast of India

Journal of Petroleum Exploration and Production Technology ◽

10.1007/s13202-019-00777-4 ◽

2019 ◽

Vol 10 (3) ◽

pp. 911-918

Author(s):

Biplab Kumar Mukherjee ◽

G. Karthikeyan ◽

Karanpal Rawat ◽

Hari Srivastava

Keyword(s):

Seismic Data ◽

East Coast ◽

Velocity Model ◽

P Wave ◽

S Wave ◽

Gardner Equation ◽

East Coast Of India ◽

Nonlinear Fitting ◽

Sonic Log ◽

Mahanadi Basin

Abstract Shale is the primary rock type in the shallow marine section of the Mahanadi Basin, East Coast of India. Shale, being intrinsically anisotropic, always affects the seismic data. Anisotropy derived from seismic and VSP has lower resolution and mostly based on P wave. The workflow discussed here uses Gardner equation to derive vertical velocity and uses a nonlinear fitting to extract the Thomsen’s parameters using both the P wave and S wave data. These parameters are used to correct the sonic log of a deviated well as well as anisotropic AVO response of the reservoir. The presence of negative delta was observed, which is believed to be affected by the presence of chloride and illite in the rock matrix. This correction can be used to update the velocity model for time–depth conversion and pore pressure modelling.

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Prestack 2D parsimonious Kirchhoff depth migration of elastic seismic data

Geophysics ◽

10.1190/1.3581359 ◽

2011 ◽

Vol 76 (4) ◽

pp. S157-S164 ◽

Cited By ~ 6

Author(s):

Robert Sun ◽

George A. McMechan

Keyword(s):

Seismic Data ◽

Velocity Model ◽

P Wave ◽

P Value ◽

Common Source ◽

S Wave ◽

P Values ◽

Depth Migration ◽

Reflector Surface ◽

Kirchhoff Depth Migration

We have extended prestack parsimonious Kirchhoff depth migration for 2D, two-component, reflected elastic seismic data for a P-wave source recorded at the earth’s surface. First, we separated the P-to-P reflected (PP-) waves and P-to-S converted (PS-) waves in an elastic common-source gather into P-wave and S-wave seismograms. Next, we estimated source-ray parameters (source p values) and receiver-ray parameters (receiver p values) for the peaks and troughs above a threshold amplitude in separated P- and S-wavefields. For each PP and PS reflection, we traced (1) a source ray in the P-velocity model in the direction of the emitted ray angle (determined by the source p value) and (2) a receiver ray in the P- or S-velocity model back in the direction of the emergent PP- or PS-wave ray angle (determined by the PP- or PS-wave receiver p value), respectively. The image-point position was adjusted from the intersection of the source and receiver rays to the point where the sum of the source time and receiver-ray time equaled the two-way traveltime. The orientation of the reflector surface was determined to satisfy Snell’s law at the intersection point. The amplitude of a P-wave (or an S-wave) was distributed over the first Fresnel zone along the reflector surface in the P- (or S-) image. Stacking over all P-images of the PP-wave common-source gathers gave the stacked P-image, and stacking over all S-images of the PS-wave common-source gathers gave the stacked S-image. Synthetic examples showed acceptable migration quality; however, the images were less complete than those produced by scalar reverse-time migration (RTM). The computing time for the 2D examples used was about 1/30 of that for scalar RTM of the same data.

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Crustal structure and evolution of the Niuafo'ou Microplate in the northeastern Lau Basin, Southwestern Pacific

10.5194/egusphere-egu2020-1404 ◽

2020 ◽

Author(s):

Florian Schmid ◽

Heidrun Kopp ◽

Michael Schnabel ◽

Anke Dannowski ◽

Ingo Heyde ◽

...

Keyword(s):

Gravity Data ◽

Seafloor Spreading ◽

P Wave ◽

Spreading Center ◽

Plate Boundaries ◽

Volcanic Arc ◽

Lau Basin ◽

Refraction Seismic ◽

Wave Tomography ◽

Back Arc

The northeastern Lau Basin is one of the fastest opening and magmatically most active back-arc regions on Earth. Although the current pattern of plate boundaries and motions in this complex mosaic of microplates is fairly well understood, the structure and evolution of the back-arc crust are not. We present refraction seismic, multichannel seismic and gravity data from a 300 km long east-west oriented transect crossing the Niuafo&#8217;ou Microplate (back-arc), the Fonualei Rift and Spreading Centre (FRSC) and the Tofua Volcanic Arc at 17&#176;20&#8217;S. Our P wave tomography model shows strong lateral variations in the thickness and velocity-depth distribution of the crust. The thinnest crust is present in the Fonualei Rift and Spreading Center, suggesting active seafloor spreading there. In the much thicker crust of the volcanic arc we identify a region of anomalously low velocities, indicative of partial melts. Surprisingly, the melt reservoir is located at ~17 km distance to the volcanic front, supporting the hypothesis that melts are deviated from the volcanic arc towards the FRSC in sub-crustal domains. We identify two distinct regions in the back-arc crust, representing different opening phases of the northeastern Lau Basin. During initial extension, likely dominated by rifting, crust of generally lower upper-crustal velocities formed. During an advanced opening phase, likely dominated by seafloor spreading, crust of higher upper-crustal velocities formed and is now up to 11 km thick. This thickening is the result of magmatic underplating, which is supported by elevated upper mantle temperatures in this region.

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Seismic P Wave Velocity Model From 3‐D Surface and Borehole Seismic Data at the Alpine Fault DFDP‐2 Drill Site (Whataroa, New Zealand)

10.26686/wgtn.13819346 ◽

2021 ◽

Author(s):

V Lay ◽

S Buske ◽

SB Bodenburg ◽

John Townend ◽

R Kellett ◽

...

Keyword(s):

New Zealand ◽

Wave Velocity ◽

Seismic Data ◽

Velocity Model ◽

P Wave ◽

Alpine Fault ◽

P Wave Velocity ◽

Drill Site ◽

Borehole Seismic

No description supplied

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Structure of oceanic crust in back-arc basins modulated by mantle source heterogeneity

Geology ◽

10.1130/g48407.1 ◽

2020 ◽

Author(s):

Ingo Grevemeyer ◽

Shuichi Kodaira ◽

Gou Fujie ◽

Narumi Takahashi

Keyword(s):

Oceanic Crust ◽

Mantle Source ◽

Seismic Data ◽

Lower Crust ◽

Subduction Zones ◽

P Wave ◽

Spreading Ridge ◽

Volcanic Arc ◽

Depleted Mantle ◽

Back Arc

Subduction zones may develop submarine spreading centers that occur on the overriding plate behind the volcanic arc. In these back-arc settings, the subducting slab controls the pattern of mantle advection and may entrain hydrous melts from the volcanic arc or slab into the melting region of the spreading ridge. We recorded seismic data across the Western Mariana Ridge (WMR, northwestern Pacific Ocean), a remnant island arc with back-arc basins on either side. Its margins and both basins show distinctly different crustal structure. Crust to the west of the WMR, in the Parece Vela Basin, is 4–5 km thick, and the lower crust indicates seismic P-wave velocities of 6.5–6.8 km/s. To the east of the WMR, in the Mariana Trough Basin, the crust is ~7 km thick, and the lower crust supports seismic velocities of 7.2–7.4 km/s. This structural diversity is corroborated by seismic data from other back-arc basins, arguing that a chemically diverse and heterogeneous mantle, which may differ from a normal mid-ocean-ridge–type mantle source, controls the amount of melting in back-arc basins. Mantle heterogeneity might not be solely controlled by entrainment of hydrous melt, but also by cold or depleted mantle invading the back-arc while a subduction zone reconfigures. Crust formed in back-arc basins may therefore differ in thickness and velocity structure from normal oceanic crust.

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3D P-wave velocity model of Ireland's crust from controlled source tomography

10.5194/egusphere-egu2020-18510 ◽

2020 ◽

Author(s):

Senad Subašić ◽

Meysam Rezaeifar ◽

Nicola Piana Agostinetti ◽

Sergei Lebedev ◽

Christopher Bean

Keyword(s):

Wave Velocity ◽

Velocity Model ◽

P Wave ◽

Uppermost Mantle ◽

Data Set ◽

Location Uncertainty ◽

P Wave Velocity ◽

1D Model ◽

Minimum 1D Model ◽

1D Velocity Model

We present a 3D P-wave velocity model of the crust and uppermost mantle below Ireland. In the absence of local earthquakes, we used quarry and mining blasts recorded on permanent stations in the Irish National Seismic Network (INSN) and during various temporary deployments. We compiled a database of 1,100 events and around 20,000 P-wave arrivals, with each event associated with a known quarry. The source location uncertainty is therefore minimal. Both source and receiver locations are fixed in time and we used repeating events to estimate the travel time uncertainty for each source-receiver combination. We created a starting 1D velocity model from previously available data, and then used VELEST to calculate a preliminary minimum 1D velocity model. The 1D velocity model enabled us to remove outliers from the data set, and to calculate the final minimum 1D model used as the initial model in the 3D tomographic inversion. The resulting 3D P-wave velocity model will shed new light on the 3D crustal structure of Ireland.

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Using 2D long-streamer seismic data waveform tomography to decipher sedimentary record of fault activity

10.5194/egusphere-egu2020-9073 ◽

2020 ◽

Author(s):

Amin Kahrizi ◽

Matthias Delescluse ◽

Mathieu Rodriguez ◽

Pierre-Henri Roche ◽

Anne Becel ◽

...

Keyword(s):

Mass Transport ◽

Seismic Data ◽

Velocity Model ◽

P Wave ◽

Fault System ◽

Fault Activity ◽

Traveltime Tomography ◽

P Wave Velocity ◽

Waveform Tomography ◽

Mass Transport Deposits

Acoustic full-waveform inversion (FWI), or waveform tomography, involves use of both phase and amplitude of the recorded compressional waves to obtain a high-resolution P-wave velocity model of the propagation medium. Recent theoretical and computing advances now allow the application of this highly non-linear technique to field data. This led to common use of the FWI for industrial purposes related to reservoir imaging, physical properties of rocks, and fluid flow. Application of FWI in the academic domain has, so far, been limited, mostly because of the lack of adequate seismic data. While refraction seismic datasets include large source-receiver offsets that are useful to find a suitable starting velocity model through traveltime tomography, these acquisitions rarely reach the high density of receivers necessary for waveform tomography. On the other hand, multichannel seismic (MCS) reflection data acquisition has a dense receiver spacing but only modern long-streamer data have offsets that, in some cases, enable constraining subsurface velocities at a significant enough depth to be useful for structural or tectonic purposes.In this study, we show how FWI can help decipher the record of a fault activity through time at the Shumagin Gap in Alaska. The MCS data were acquired on RV Marcus G. Langseth during the ALEUT cruise in the summer of 2011 using two 8-km-long seismic streamers and a 6600 cu. in. tuned airgun array. One of the most noticeable reflection features imaged on two profiles is a large, landward-dipping normal fault in the overriding plate; a structural configuration making the area prone to generating both transoceanic and local tsunamis, including from landslides. This fault dips ~40&#176;- 45&#176;, cuts the entire crust and connects to the plate boundary fault at ~35 km depth, near the intersection of the megathrust with the forearc mantle wedge. The fault system reaches the surface at the shelf edge 75 km from the trench, forming the Sanak basin where the record of the recent activity of the fault is not clear. Indeed, contouritic currents tend to be trapped by the topography created by faults, even after they are no longer active.&#160; Erosion surfaces and onlaps from contouritic processes as well as gravity collapses and mass transport deposits results in complex structures that make it challenging to evaluate the fault activity. The long streamers used facilitated recording of refraction arrivals in the target continental slope area, which permitted running streamer traveltime tomography followed by FWI to produce coincident detailed velocity profiles to complement the reflection sections. FWI imaging of the Sanak basin reveals low velocities of mass transport deposits and velocity inversions indicate mechanically weak layers linking some faults to gravity sliding on a d&#233;collement. These details question previous interpretation of a present-day active fault. Our goal is to further analyze the behavior of the fault system using the P-wave velocity models from FWI to quantitatively detect fluids and constrain sediment properties.

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