Full-waveform inversion at Santorini volcano

2020 ◽  
Author(s):  
Kajetan Chrapkiewicz ◽  
Michele Paulatto ◽  
Joanna Morgan ◽  
Mike Warner ◽  
Benjamin Heath ◽  
...  
Keyword(s):  
Travel Time ◽  
Waveform Inversion ◽  
Hydrothermal Systems ◽  
P Wave ◽  
Detailed Knowledge ◽  
Full Waveform Inversion ◽  
Low Velocity ◽  
Full Waveform ◽  
Travel Time Tomography ◽  
Air Gun

<p>Detailed knowledge about geometry and physical properties of magmatic systems at arc volcanoes promises to better constrain models of magma differentiation, transit and storage in the crust, and to help assess volcanic hazard.</p><p>Unfortunately, low-velocity zones associated with melt accumulation are particularly difficult to image by conventional travel-time tomography due to its limited resolving power, resulting in blurred boundaries and underestimated velocity contrasts.</p><p>Here we alleviate these issues by applying full-waveform inversion (FWI) to study a magmatic system of Santorini - an active, semi-submerged volcano with a known record of large, caldera-forming eruptions.</p><p>We use a 3D wide-angle, multi-azimuth seismic dataset from the recent PROTEUS experiment acquired with ca. 150 ocean-bottom/land seismic stations and ca. 14,000 air-gun shots. We implement a finite-difference immersed boundary method to simulate reflections off the caldera’s irregular topography, and pressure-velocity conversion to take full advantage of the multi-component data. We perform inversion with careful data-selection, increasing frequency up to 6 Hz, and extensive quality-control based on a phase spatial-continuity criterion.</p><p>A final P-wave velocity model of the upper crust offers a high-resolution image of Santorini magmatic and hydrothermal systems with pronounced low-velocity zones due to a high melt and water content respectively. The features are better resolved and the velocity contrasts distinctly sharper than in the starting model obtained with travel-time tomography. We also recover a previously undetected low velocity anomaly of >40% beneath Kolumbo - a submarine volcanic cone to the NE of Santorini caldera. We interpret this anomaly as a magmatic sill.</p>

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

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.

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

Solid Earth ◽  
2019 ◽  
Vol 10 (6) ◽  
pp. 1833-1855
Author(s):  
Clàudia Gras ◽  
Daniel Dagnino ◽  
Clara Estela Jiménez-Tejero ◽  
Adrià Meléndez ◽  
Valentí Sallarès ◽  
...  
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 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.

Lower crustal structures at Rockall Trough (west of Ireland) by Full waveform inversion

2020 ◽  
Author(s):  
Gaurav Tomar ◽  
Christopher J. Bean ◽  
Satish C. Singh
Keyword(s):  
Travel Time ◽  
Seismic Data ◽  
High Velocity ◽  
Waveform Inversion ◽  
Velocity Model ◽  
Full Waveform Inversion ◽  
Data Set ◽  
Full Waveform ◽  
Travel Time Tomography ◽  
Rockall Trough

<p>Rockall trough lies to the west of Ireland in NE Atlantic, it has a complex geology and has been debated for controversial geology for more than two decades. We have performed Full waveform inversion (FWI) on 2D seismic data set that is recorded in 2013-14 by using 10 km long streamer, this 2D seismic line is situated near the North-West margin in the Rockall Bank area. Full waveform inversion (FWI) is a powerful technique for obtaining elastic properties of the sub-surface from the seismic data. FWI provides properties of the sub-surface at the scale of the wavelength of the data set. We used travel time tomography on downward extrapolated data set to obtain a smooth starting velocity model for FWI. Downward continuation is a technique that enhances the first arrival and also reduces the computation time for forward modelling in FWI. The velocity model obtained from refraction travel time tomography, indicates the velocity from 1.6-4 km/s for the sediments and we have also observed very high velocity ~ 6-7.5 km/s just 3 km below sea-floor. We have performed FWI using these TTT velocity model as a starting model and inverted the refractions along with the wide angle reflections in the frequency range of 3-10 hz. FWI results gives the velocity of 6-7.2 km/s as well as defines geological structures that can be seen in the migrated seismic section. These high velocity structures could be a part of the continental crust and/or lower oceanic crustal igneous rocks like Gabbro.</p>

Multi-parameter model building for the Qiuyue structure using four-component ocean-bottom seismometer data

Geophysics ◽  
2021 ◽  
pp. 1-52
Author(s):  
Yuzhu Liu ◽  
Xinquan Huang ◽  
Jizhong Yang ◽  
Xueyi Liu ◽  
Bin Li ◽  
...  
Keyword(s):  
Wave Velocity ◽  
Waveform Inversion ◽  
Velocity Model ◽  
P Wave ◽  
Velocity Analysis ◽  
Full Waveform Inversion ◽  
Ocean Bottom ◽  
Ocean Bottom Seismometer ◽  
Full Waveform ◽  
P Wave Velocity

Thin sand-mud-coal interbedded layers and multiples caused by shallow water pose great challenges to conventional 3D multi-channel seismic techniques used to detect the deeply buried reservoirs in the Qiuyue field. In 2017, a dense ocean-bottom seismometer (OBS) acquisition program acquired a four-component dataset in East China Sea. To delineate the deep reservoir structures in the Qiuyue field, we applied a full-waveform inversion (FWI) workflow to this dense four-component OBS dataset. After preprocessing, including receiver geometry correction, moveout correction, component rotation, and energy transformation from 3D to 2D, a preconditioned first-arrival traveltime tomography based on an improved scattering integral algorithm is applied to construct an initial P-wave velocity model. To eliminate the influence of the wavelet estimation process, a convolutional-wavefield-based objective function for the preprocessed hydrophone component is used during acoustic FWI. By inverting the waveforms associated with early arrivals, a relatively high-resolution underground P-wave velocity model is obtained, with updates at 2.0 km and 4.7 km depth. Initial S-wave velocity and density models are then constructed based on their prior relationships to the P-wave velocity, accompanied by a reciprocal source-independent elastic full-waveform inversion to refine both velocity models. Compared to a traditional workflow, guided by stacking velocity analysis or migration velocity analysis, and using only the pressure component or other single-component, the workflow presented in this study represents a good approach for inverting the four-component OBS dataset to characterize sub-seafloor velocity structures.

Amplitude-based misfit functions in viscoelastic full-waveform inversion applied to walk-away vertical seismic profile data

Geophysics ◽  
2019 ◽  
Vol 84 (5) ◽  
pp. B335-B351 ◽  
Author(s):  
Wenyong Pan ◽  
Kristopher A. Innanen
Keyword(s):  
Amplitude Ratio ◽  
Waveform Inversion ◽  
Seismic Profile ◽  
P Wave ◽  
Western Canada ◽  
Full Waveform Inversion ◽  
Walk Away ◽  
Profile Data ◽  
S Wave ◽  
Full Waveform

Viscoelastic full-waveform inversion is applied to walk-away vertical seismic profile data acquired at a producing heavy-oil field in Western Canada for the determination of subsurface velocity models (P-wave velocity [Formula: see text] and S-wave velocity [Formula: see text]) and attenuation models (P-wave quality factor [Formula: see text] and S-wave quality factor [Formula: see text]). To mitigate strong velocity-attenuation trade-offs, a two-stage approach is adopted. In Stage I, [Formula: see text] and [Formula: see text] models are first inverted using a standard waveform-difference (WD) misfit function. Following this, in Stage II, different amplitude-based misfit functions are used to estimate the [Formula: see text] and [Formula: see text] models. Compared to the traditional WD misfit function, the amplitude-based misfit functions exhibit stronger sensitivity to attenuation anomalies and appear to be able to invert [Formula: see text] and [Formula: see text] models more reliably in the presence of velocity errors. Overall, the root-mean-square amplitude-ratio and spectral amplitude-ratio misfit functions outperform other misfit function choices. In the final outputs of our inversion, significant drops in the [Formula: see text] to [Formula: see text] ratio (~1.6) and Poisson’s ratio (~0.23) are apparent within the Clearwater Formation (depth ~0.45–0.50 km) of the Mannville Group in the Western Canada Sedimentary Basin. Strong [Formula: see text] (~20) and [Formula: see text] (~15) anomalies are also evident in this zone. These observations provide information to help identify the target attenuative reservoir saturated with heavy-oil resources.

Sign in / Sign up

Export Citation Format

Share Document