A5103216288- Seismic Waves and Analysis
- Seismic Imaging and Inversion Techniques
- Seismology and Earthquake Studies
- earthquake and tectonic studies
- Planetary Science and Exploration
- Geological and Geophysical Studies Worldwide
- High-pressure geophysics and materials
- Geophysics and Sensor Technology
- Geological and Geochemical Analysis
- Earthquake Detection and Analysis
- Underwater Acoustics Research
- Astro and Planetary Science
- Geological and Tectonic Studies in Latin America
- Geological and Geophysical Studies
- Geology and Paleoclimatology Research
- Archaeological and Historical Studies
- Cryospheric studies and observations
- Landslides and related hazards
- Geophysical Methods and Applications
- Methane Hydrates and Related Phenomena
- Image and Signal Denoising Methods
- Structural Health Monitoring Techniques
- Geophysical and Geoelectrical Methods
- Power Quality and Harmonics
- Advanced Electrical Measurement Techniques
Geociencias Barcelona
2015-2024
University Medical Center Freiburg
2024
Leiden University Medical Center
2022
Emory University
2020-2022
University of Beira Interior
2021
Instituto de Telecomunicações
2021
Islamic Azad University, Science and Research Branch
2021
Instituto Politécnico de Lisboa
2021
University of Lisbon
2021
University of Tehran
2021
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...
[1] Noise with periods 3 to 10 s, ubiquitous in seismic records, is expected be mostly generated by pairs of ocean wave trains opposing propagation directions half the frequency. Here we present first comprehensive numerical model microseismic generation random waves, including reflections. Synthetic and observed spectra are well correlated (r > 0.85). On basis results, noise events can clustered three broad classes: wind waves a directional spectrum (class I), sea states significant...
Stacks of ambient noise cross-correlations are more and routinely used to extract empirical Green's functions between station pairs. The success the is due waves which recorded by both stations that constructively sum at lag times equal their propagation time pair. Stacking cross-correlograms corresponding different spans improves azimuthal coverage further enhances signals. Here we show how instantaneous phase coherence can be for a efficient signal extraction from cross-correlations....
Clues to a planet's geologic history are contained in its interior structure, particularly core. We detected reflections of seismic waves from the core-mantle boundary Mars using InSight data and inverted these together with geodetic constrain radius liquid metal core 1830 ± 40 kilometers. The large implies martian mantle mineralogically similar terrestrial upper transition zone but differing Earth by not having bridgmanite-dominated lower mantle. inferred mean density 5.7 6.3 grams per...
Single seismometer structure Because of the lack direct seismic observations, interior Mars has been a mystery. Khan et al. , Knapmeyer-Endrun and Stähler used recently detected marsquakes from deployed during InSight mission to map (see Perspective by Cottaar Koelemeijer). likely 24- 72-kilometer-thick crust with very deep lithosphere close 500 kilometers. Similar Earth, low-velocity layer probably exists beneath lithosphere. The is highly enriched in radioactive elements that help heat...
The S-transform is becoming popular for time-frequency analysis and data-adaptive filtering thanks to its simplicity. While this transform works well in the continuous domain, discrete version may fail achieve accurate results. This paper compares contrasts with better known wavelet transform, defines a relation between both. connection allows understanding of S-transform, makes it possible employ reconstruction formula as new inverse propose several methods solve some main limitations such...
In the absence of earthquakes, oceanic microseisms are strongest signals recorded by seismic stations. Using GEOSCOPE global network, we show that secondary microseism spectra have characteristics depend on station latitude and season. both hemispheres, noise amplitude is larger during local winter, close to equator, stable over year. There an excellent correlation between variations year changes in highest wave areas. Considering polarization microseisms, stations Northern Hemisphere...
The strongest seismic noise, called secondary microseisms, is generated by ocean wave interactions and we model this noise using the theory of Longuet-Higgins generalized to random gravity waves. Noise sources are computed with an that takes into account coastal reflections. Variations source locations consistent seasonal variations spectra. spectra modelled over many years for stations representative various environments such as continent, island polar area constrain, each environment,...
Abstract The instrument package SEIS (Seismic Experiment for Internal Structure) with the three very broadband and short‐period seismic sensors is installed on surface Mars as part of NASA's InSight Discovery mission. When compared to terrestrial installations, deployed in a harsh wind temperature environment that leads inevitable degradation quality recorded data. One ubiquitous artifact raw data an abundance transient one‐sided pulses often accompanied by high‐frequency spikes. These...
The InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission landed on the surface of Mars November 26, 2018. One scientific instruments in payload that is essential to SEIS package (Seismic Experiment for Interior Structure) which includes a very broadband short period seismometer. More than one year since landing, continues be fully operational has been collecting an exceptional data set contains not only signals seismic origins, but also noise...
We detected surface waves from two meteorite impacts on Mars. By measuring group velocity dispersion along the impact-lander path, we obtained a direct constraint crustal structure away InSight lander. The crust north of equatorial dichotomy had shear wave approximately 3.2 kilometers per second in 5- to 30-kilometer depth range, with little variation. This implies higher density than inferred beneath lander, suggesting either compositional differences or reduced porosity volcanic areas...
Abstract For over three Earth years the Marsquake Service has been analyzing data sent back from Seismic Experiment for Interior Structure—the seismometer placed on surface of Mars by NASA’s InSight lander. Although October 2021, seismic catalog included 951 events, until recently all these events have assessed as lying within a radius 100° InSight. Here we report two distant that occurred days each other, located far side Mars, giving us our first glimpse into Mars’ core shadow zone. The...
We present the first observations of seismic waves propagating through core Mars. These observations, made using data collected by InSight geophysical mission, have allowed us to construct seismically constrained models for elastic properties Mars' core. observe core-transiting phase SKS from two farside events detected on Mars and measure travel times relative mantle traversing body waves. travels as a compressional wave, providing information about bulk modulus density. perform...
We introduce a coherence measure for seismic signal enhancement through incoherent noise attenuation. Our processing tool is designed densely spaced arrays and identifies signals by their coherent appearance. The approach based on the determination of lateral phase as function distance, time, frequency, slowness. derived from local phases neighboring stations which we obtain analytic S‐transform. used to attenuate components in time‐frequency representations records. No waveforms are...
Abstract We present a new coherence functional to evaluate quantitatively the goodness of waveform fit between two time series as function lag time. The proposed measure is called phase cross-correlation (PCC) because it based on similarity instantaneous phases. No amplitudes are explicitly involved, and PCC therefore an amplitude unbiased measure, which equally weights every sample in correlation window. As consequence enables discriminate closely similar waveforms suited detect weak...
The S-transform provides a framework for data-adaptive filters which take advantage of time-frequency localized spectra. These basically consist in data transformation to the domain, weighting spectra, and back transformation. We illustrate that inverse manipulated spectra not necessarily transforms signals as expected from imposed weighting. time localization is directly translated spurious noise can be generated. discuss this problem suggest new S-transform, may helpful many applications...
We quantify, analyze, and characterize the frequency-dependent microseismic noise recorded by worldwide distributed seismic stations. Microseismic is generated through interaction of ocean waves. It strongest ambient noise, it observed everywhere on Earth. introduce a new approach which permits us to detect polarized signals in time-frequency domain we use noise. analyze 7 years continuous seismograms from global GEOSCOPE network. Microseisms are dominated Rayleigh waves, therefore focus...
Secondary microseisms recorded by seismic stations are generated in the ocean interaction of gravity waves. We present here theory for modelling secondary microseismic noise normal mode summation. show that sources can be modelled vertical forces and how to derive them from a realistic wave model. then compute bathymetry excitation effect earth model using modes comparison with Longuet–Higgins approach. The strongest areas oceans depends on period different each mode. Seismic is summation...
Secondary microseismic noise is generated by non-linear interactions between ocean waves at the surface. We present here theory for computing site effect of layer upon body sources distributed along By defining wavefield as superposition plane waves, we show that can be described constructive interference multiply reflected P in are then converted to either or SV ocean–crust interface. observe varies strongly with period and depth, although a different way than Rayleigh waves. also stronger...
We present a new upper-mantle tomographic model derived solely from hum seismic data. Phase correlograms between station pairs are computed to extract phase-coherent signals. Correlograms then stacked using the time–frequency phase-weighted stack method build-up empirical Green's functions. Group velocities and uncertainties measured in wide period band of 30–250 s, following resampling approach. Less data required reliable group at short periods than long periods, 2 yr necessary measure for...
Abstract The collapse of a mine tailings dam and subsequent flood in SE Brazil on 5 November 2015 was preceded by small‐magnitude seismic sequence. In this report, we explore the spatiotemporal associations between events accident discuss their possible connection. We also analyze signals generated turbulent mudflow, as recorded Brazilian Seismographic Network (RSBR). light our observations, propose contributing factor for either ground shaking and/or soil liquefaction triggered earthquakes....
Abstract Single‐station autocorrelations of seismic ambient noise allow to obtain the shallow subsurface reflection response without need any active source or earthquake. Recently, crustal‐scale studies successfully applied this method map crust‐mantle boundary. These employed different processing methodologies stabilize and identify weak‐amplitude reflections. Here we also analyze but use higher‐frequency bands basement Ebro Basin in Spain. This basin has a nonuniform structure due its...
Stacks of ambient noise correlations are routinely used to extract empirical Green’s functions (EGFs) between station pairs. The time–frequency phase-weighted stack (tf-PWS) is a physically intuitive nonlinear denoising method that uses the phase coherence improve EGF convergence when performance conventional linear averaging methods not sufficient. high computational cost continuous approach transformation currently main limitation in studies. We introduce time-scale (ts-PWS) as an...