A5044669071- Seismic Waves and Analysis
- High-pressure geophysics and materials
- earthquake and tectonic studies
- Seismic Imaging and Inversion Techniques
- Geological and Geochemical Analysis
- Seismology and Earthquake Studies
- Geophysics and Sensor Technology
- Earthquake Detection and Analysis
- Underwater Acoustics Research
- Geological and Geophysical Studies
- Geological formations and processes
- Hydraulic Fracturing and Reservoir Analysis
- Geophysical and Geoelectrical Methods
- Geological and Geophysical Studies Worldwide
- Geophysical Methods and Applications
- Geology and Paleoclimatology Research
- Methane Hydrates and Related Phenomena
- Geophysics and Gravity Measurements
- Reservoir Engineering and Simulation Methods
- Geochemistry and Geologic Mapping
- Inorganic Fluorides and Related Compounds
- Magnesium Oxide Properties and Applications
- Computer Graphics and Visualization Techniques
- Cerebrospinal fluid and hydrocephalus
- Geological Formations and Processes Exploration
Utrecht University
2015-2024
We present a new tool for efficient incoherent noise reduction array data employing complex trace analysis. An amplitude-unbiased coherency measure is designed based on the instantaneous phase, which used to weight samples of an ordinary, linear stack. The result called phase-weighted stack (PWS) and cleaned from noise. PWS thus permits detection weak but coherent arrivals. method presented can easily be extended cross-correlations or applied in τp domain. illustrate discuss advantages...
Regional seismic tomography provides valuable information on the structure of shields, thereby gaining insight to formation and stabilization old continents. Fennoscandia (known as Baltic Shield for its exposed part) is a composite shield which last recorded tectonic event intrusion Rapakivi granitoids around 1.6 Ga. A experiment carried out part European project Svecofennian‐Karelia‐Lapland‐Kola (SVEKALAPKO) was designed study upper mantle Finnish Shield, especially boundary between Archean...
The fine structure of the upper mantle discontinuities is investigated using observations converted waves on short‐period and broadband seismograms. Using a stacking technique to analyze P wave coda teleseismic records, evidence found for coherent near‐receiver ‐to‐ S phases generated by 400‐ 670‐km discontinuity beneath number stations used in this study. Variations travel time, slowness, amplitude these as observed among stacks Regional Seismic Test Network United States Autonomously...
The upper mantle velocity structure beneath Europe is investigated by body-wave modelling of broad-band seismograms from earthquakes in the eastern Mediterranean recorded stations north-west Europe. gross features P- and S-wave distribution as inferred data show a high lid, low zone, two discontinuities at depths approximately 420 650 km. also present evidence for lateral heterogeneity least few per cent (2.5 P, 4 S) to depth 400 Many variations can be related tectonic setting region between...
Although the Earth’s inner core has long been thought to be solid, there have not, as yet, unequivocal observations of shear waves. Here we present phases pPKJKP and SKJKP for Flores Sea event 1996 June 17. The support value approximately 3.6 km s− 1 wave velocity open up new possibilities exploring anisotropic structure attenuation properties core. analysis validation observation is based on a method that can used in search identification In this normal mode synthetics solid are compared...
We measured interstation fundamental mode Rayleigh wave phase velocities using data from the NARS‐Baja seismic network located around Gulf of California. A region‐average, shear velocity model and a set azimuthally anisotropic maps are obtained these data. The average structure shows strong low‐velocity zone underlying thin lid suggestive low down into transition zone. display signatures sedimentary layers, crustal thickness variations, upwelling under plate boundary, presence subducted...
During thunderstorm activity in the Netherlands, electromagnetic and infrasonic signals are emitted due to process of lightning thunder. It is shown that correlating infrasound detections with results from a detection network successful up distances 50 km array. Infrasound recordings clearly show blastwave characteristics which can be related cloud‐ground discharges, dominant frequency between 1–5 Hz. Amplitude measurements CG discharges partly explained by beam pattern line source 3.9 Hz,...
Abstract We present the first nationwide crustal thickness and Vp/Vs maps for Botswana based on analysis of new P wave receiver functions NARS‐Botswana network integrated with previous function results in Botswana. Using H‐K analysis, we found values ranging from 34 km Okavango Rift Zone to 49 at border between Magondi Belt Zimbabwe Craton. For stations significant sediment cover, a correction was applied sequential stacking. observed distinct differences Kaapvaal craton. The eastern part...
We present a method for the computation of finite-frequency sensitivity kernels two-station surface wave measurements. It is based on combination spectral-element modelling seismic propagation, adjoint techniques and traveltime estimates from cross-correlations seismograms. The analysis 1-D earth model resulted in two major conclusions: (1) zero along interstation ray path group velocity measurements obtained by cross-correlations. follows that should not be made cross-correlation if...
Abstract Rayleigh wave group and phase velocity measurements obtained from ambient noise earthquake data at 51 broadband stations were used to construct the first 3‐D crustal upper mantle shear model of Botswana. The shows low velocities associated with Passarge Nosop sedimentary basins, whereas Kaapvaal, Zimbabwe, Maltahohe, Congo Cratons are recognized by high velocities. lowest velocity, beneath northeastern Botswana, is southwestern branch East African Rift System. This low‐velocity...
Splitting of SKS waves caused by anisotropy may be analyzed measuring the splitting intensity, i.e., amplitude transverse signal relative to radial in time window.This quantity is simply related structural parameters.Extending widely used cross-correlation method for travel-time anomalies anisotropic problems, we propose measure SKSsplitting intensity a robust that can automated build large high-quality datasets.For weak anisotropy, SKS-splitting retrieved cross-correlating with sum and...
Abstract The province of Groningen in the Netherlands holds one world's largest natural gas fields, and it has been an important source energy for Western Europe many decades. seismicity recent years called a better understanding local subsurface, therefore dense network 70 boreholes was installed early 2015. Each borehole is equipped with four geophones surface accelerometer. In this study, data from are used to determine shallow velocity structure that quantification seismic hazard...
An international, interdisciplinary project, which 2 years ago deployed the largest dense seismic antenna ever in Europe, expects next to present important findings on lithosphere and asthenosphere of a portion Trans‐European Suture Zone (TESZ). Final processing is currently under way data from array 120 seismographs along 900‐km‐long by 100‐km‐wide strip Gottingen, Germany, south, through Denmark, Stockholm, Sweden north, across northwestern part TESZ (Figure 1). Project Tor teleseismic...
This work presents the first comprehensive 3-D model of crust beneath The Netherlands. To obtain this model, we designed NARS-Netherlands project, a dense deployment broadband stations in area. Rayleigh and Love wave group velocity dispersion was measured from ambient noise cross-correlations. Azimuthally anisotropic maps were then constructed isotropic part used to determine shear speed that includes effects radial anisotropy. Employing Neighbourhood Algorithm for depth inversion, obtained...
Abstract New broadband seismic data from Botswana and South Africa have been combined with existing the region to develop improved P S wave velocity models for investigating upper mantle structure of southern Africa. Higher craton‐like velocities are imaged beneath Rehoboth Province parts northern Okwa Terrane Magondi Belt, indicating that edge greater Kalahari Craton lithosphere lies along boundary these terranes. Lower off‐craton Damara‐Ghanzi‐Chobe may in part reflect thinning incipient...
The Gulf of California rift forms a geologically young and active plate boundary that links the San Andreas strike‐slip fault system in to oceanic spreading East Pacific Rise. Although this is classical example transform‐rift boundary, tectonic evolution surrounding regions complex poorly understood due lack geological geophysical data. In 2002, Network Autonomously Recording Seismographs(NARS)‐Baja network was installed.lt consists 19 broadband seismic stations deployed Baja‐California...
A time- and frequency-dependent polarization method is applied to synthetic observational data in order investigate effects of lateral heterogeneity on surface wave polarization. It shown that interference signals can produce artifacts the as determined for dominant signal present data. The technique waves recorded Iberia character wavetrains. Rayleigh with a southwest backazimuth south Spain appear strongly attenuated relative other locations Iberia. By analysing their polarizations, it be...
Several registrations of teleseismic events on the NARS array show a phase which can be identified as P to S conversion at 670‐km discontinuity beneath western Europe. Variations in amplitude and arrival time so‐called Ps are observed for different azimuths. A single station/multiple event stacking technique was applied data determine consistency phase. The results indicative amplitude, time, slowness variations converted local scale. These observations most logically explained by model with...
Abstract We present a 3D shear‐wave velocity model of the southern African upper mantle developed using 30–200 s period Rayleigh waves recorded on regional seismic networks spanning subcontinent. The shows high velocities (∼4.7–4.8 km/s) at depths 50–250 km beneath Archean nucleus and several surrounding Paleoproterozoic Mesoproterozoic terranes, placing margin greater Kalahari Craton along boundary Damara Belt eastern boundaries Gariep Namaqua‐Natal belts. At ≥250 km, there is little...
The accurate timing of seismological data is crucial for most quantitative examinations in seismology. We present evidence that traveltime from many stations contain systematic variations which can be identified by checking the median station delay times as a function time. This expected to constant but deviations are found. Several hundred report arrival ISC have been examined. almost 8 per cent these show changes more than 1s and thus exceed structural signal data. Temporal 0.5–1s common....
Shear wave splitting measurements were made for local earthquakes in southern California at incidence angles larger than the critical angle. For region of San Bernardino Mountains, fast polarization directions vary strongly, but are consistently roughly perpendicular to ray paths. This observation is most readily explained by transverse isotropy with a vertical symmetry axis, and probably associated horizontally foliated gneisses or schists upper crust. Other show predominance north‐south...
The Tyrrhenian Sea in the Mediterranean formed as result of roll-back Adriatic and Ionian subducting plates. It is mostly underlain by strongly thinned continental lithosphere, but contains two small oceanic basins southern Tyrrhenian, youngest one located just behind active magmatic arc. Its regional setting with dense station coverage provides a unique opportunity to derive high-resolution, 3-D shear-velocity model this back-arc basin surrounding onshore areas using interstation...