scholarly journals A new 1D velocity model and absolute locations image the Mayotte seismo-volcanic region

2021 ◽  
pp. 107440
Author(s):  
Aude Lavayssière ◽  
Wayne Crawford ◽  
Jean-Marie Saurel ◽  
Claudio Satriano ◽  
Nathalie Feuillet ◽  
...  
Keyword(s):  
Velocity Model ◽  
Volcanic Region ◽  
1D Velocity Model

Far-offset detection of normal modes and diving waves: a case study in Valhall, southern North Sea

Geophysics ◽  
2021 ◽  
pp. 1-50
Author(s):  
Filipe Borges ◽  
Martin Landrø
Keyword(s):  
Normal Modes ◽  
Seismic Source ◽  
Velocity Model ◽  
Seismic Survey ◽  
The Past ◽  
Lack Of Control ◽  
Record Data ◽  
Refracted Waves ◽  
1D Velocity Model

The use of permanent arrays for continuous reservoir monitoring has become a reality in the past decades, with Ekofisk and Valhall being its flagships. One of the possibilities when such solution is available is to passively record data while acquisitions with an active source are ongoing in nearby areas. These recordings might contain ultrafar-offset data (over 30 km), which are hardly used in standard reservoir exploration and monitoring, as they are mostly a combination of normal modes, deep reflections and diving waves. We present here data from the Valhall Life of Field Seismic array, recorded while an active seismic survey was being acquired in Ekofisk, in April 2014. Despite the lack of control on source firing time and position, analysis of the data shows that the normal modes are remarkably clear, overcoming the ambient noise in the field. The normal modes can be well explained by a two-layer acoustic model, while a combination of diving waves and refracted waves can be fairly well reproduced with a regional 1D velocity model. We suggest a method to use the far-offset recordings to monitor changes in the shallow sediments between source and receivers, both with and without a coherent seismic source in the area.

A seismotectonic study and minimum 1D velocity model for the Greater Geneva Basin, Western Switzerland

2020 ◽  
Author(s):  
Verónica Antunes ◽  
Thomas Planès ◽  
Jiří Zahradník ◽  
Anne Obermann ◽  
Celso Alvizuri ◽  
...  
Keyword(s):  
Seismic Activity ◽  
Large Scale ◽  
Detection Threshold ◽  
Velocity Model ◽  
Strike Slip ◽  
Tectonic Deformation ◽  
Geothermal Exploration ◽  
Area Of Interest ◽  
The Impact ◽  
1D Velocity Model

<p>In the framework of the Geothermie2020 project, the canton of Geneva and the Industrial Services of Geneva (SIG) are currently developing geothermal exploration in the Greater Geneva Basin (GGB), located in south-western Switzerland and neighbouring France. Before geothermal exploration begins, it is important to investigate the ongoing seismic activity, its relationship with local tectonic features, and the large-scale kinematics of the area. Background seismicity suggest that the local tectonic structures affecting the basin may still be active. Moderate-magnitude earthquakes have been identified along the Vuache fault, a major strike-slip structure crossing the basin. In this context we deployed a dense temporary network of 20 broadband stations around and within the GGB, during ~1.5 years, and reaching a detection threshold 0.5M<sub>L</sub>. </p><p>Using a new coherence-based detector (LASSIE), we detected and located 158 events in our area of interest. However, only 20 events were located in the GGB, with local magnitudes ranging from 0.7 to 2.2M<sub>L</sub>. We found no earthquakes in the Canton of Geneva where geothermal activities are taking place. We constructed a local minimum 1D velocity model with VELEST, using the recorded seismicity together with earthquakes from adjacent regions, in a total of 1263 P- and S-picks. The new velocity model allowed to relocate micro-seismic activity up to 11km depth along the main fault systems (i.e. Vuache, Cruseilles, Le Coin, and Arve) offsetting the GGB. We retrieved 8 new focal mechanisms for the area, using a combination of polarities and waveform inversion techniques (CSPS method). A stress inversion shows a tectonic deformation dominated by a quasi-pure strike-slip regime in the GGB, consistent with structural and geological data.</p><p>The study of microseismicity in a quiet sedimentary basin is challenging due to the scarce occurrence of seismic events combined with low signal-to-noise ratios and the often strong attenuation. However, the investigation of the sporadic (yet present) natural seismicity with dedicated dense networks could provide useful information about the GGB, even with a short-term experiment. We propose a newly-computed 1D velocity model that can be used in the GGB for seismic monitoring purposes throughout the geothermal project. This model can be easily improved later on, whenever more data is available. Monitoring the evolution and dispersion of the seismic-activity through the identified seismogenic areas during the geothermal project is essential. Quantifying the seismic rate in the basin before geothermal operations start will help to quantify the impact that geothermal energy extraction might have on the GGB. </p>

Near-wellbore VSP imaging without overburden

Geophysics ◽  
2009 ◽  
Vol 74 (1) ◽  
pp. SI9-SI14 ◽  
Author(s):  
Ruiqing He ◽  
Martin Karrenbach ◽  
Bjorn Paulsson ◽  
Vlad Soutyrine
Keyword(s):  
Seismic Imaging ◽  
Velocity Model ◽  
Seismic Profile ◽  
Structural Features ◽  
Seismic Exploration ◽  
Direct Wave ◽  
Borehole Seismic ◽  
Seismic Images ◽  
Detrimental Impact ◽  
1D Velocity Model

In seismic exploration a complex overburden can cause defocused and distorted seismic images of deeper target areas. While in surface seismic imaging it is difficult to overcome this problem, vertical seismic profile (VSP) borehole seismic imaging with its well-oriented recording geometry has proven able to circumvent the overburden’s detrimental impact. Recently, VSP near-wellbore salt flank imaging without knowledge of the overburden has shown encouraging results. In this paper, we introduce another method for a more common imaging purpose: imaging near-wellbore horizons without knowledge of the overburden. A key component of our method is a reverse ray-tracing technique that uses actual VSP direct-wave traveltime picks and extrapolates through a local velocity model to obtain the direct-wave traveltimes in the vicinity of the well. The extrapolated traveltimes then serve as references for migration of the VSP reflected data from near-wellbore horizons. The merits of this method are that all source-side effects such as shot position and triggering time statics are avoided, and it can efficiently and robustly image the near-wellbore horizons because it does not need an estimated overburden velocity model prone to errors. However, the image is limited to a diamond-shaped area around the well whose size is proportional to the VSP array. A synthetic VSP experiment on the SEG/EAGE 2D overthrust model shows that this method, with a local (even an estimated 1D) velocity model, effectively images structural features, such as dip direction and discontinuities of the near-wellbore horizons.

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

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

<p>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.</p>

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

2009 ◽  
Vol 47 (6) ◽  
Author(s):  
L. De Luca ◽  
R. De Franco ◽  
G. Biella ◽  
A. Corsi ◽  
R. Tondi
Keyword(s):  
Travel Time ◽  
Velocity Model ◽  
P Wave ◽  
Wide Angle ◽  
Seismic Section ◽  
Arrival Times ◽  
First Arrival ◽  
Time Offset ◽  
Refraction Data ◽  
1D Velocity Model

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.

Probabilistic Moment Tensor Inversion for Hydrocarbon-Induced Seismicity in the Groningen Gas Field, The Netherlands, Part 1: Testing

2020 ◽  
Vol 110 (5) ◽  
pp. 2095-2111 ◽  
Author(s):  
Daniela Kühn ◽  
Sebastian Heimann ◽  
Marius P. Isken ◽  
Elmer Ruigrok ◽  
Bernard Dost
Keyword(s):  
Input Data ◽  
Moment Tensor ◽  
Good Practice ◽  
Velocity Model ◽  
Moment Tensor Inversion ◽  
Phase Identification ◽  
Moment Tensors ◽  
Velocity Models ◽  
3D Velocity Model ◽  
1D Velocity Model

ABSTRACT Since 1991, induced earthquakes have been observed and linked to gas production in the Groningen field. Recorded waveforms are complex, resulting partly from a Zechstein salt layer overlying the reservoir and partly from free-surface reverberations, internal multiples, interface conversions, guided waves, and waves diving below the reservoir. Therefore, picking of polarities or amplitudes for use in moment tensor inversion is problematic, whereas phase identification may be circumvented employing full waveform techniques. Although moment tensors have become a basic tool to analyze earthquake sources, their uncertainties are rarely reported. We introduce a method for probabilistic moment tensor estimation and demonstrate its use on the basis of a single event within the Groningen field, concentrating on detailed tests of input data and inversion parameters to derive rules of good practice for moment tensor estimation of events recorded in the Groningen field. In addition to the moment tensor, event locations are provided. Hypocenters estimated simultaneously with moment tensors are often less sensitive to uncertainties in crustal structure, which is pertinent for the application to the Groningen field, because the task of relating earthquakes to specific faults hitherto suffers from a limited resolution of earthquake locations. Because of the probabilistic approach, parameter trade-offs, uncertainties, and ambiguities are mapped. In addition, the implemented bootstrap method implicitly accounts for modeling errors affecting every station and phase differently. A local 1D velocity model extracted from a full 3D velocity model yields more consistent results than other models applied previously. For all velocity models and combinations of input data tested, a shift in location of 1 km to the south is observed for the test event compared to the public catalog. A full moment tensor computed employing the local 1D velocity model features negative isotropic components and may be interpreted as normal fault and collapse at reservoir level.

The Minimum 1D Velocity Model for the Gobi-Altai Region

2020 ◽  
Author(s):  
D. Munkhbaatar ◽  
M. Adiya ◽  
T. Khuut
Keyword(s):  
Velocity Model ◽  
Altai Region ◽  
1D Velocity Model
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