scholarly journals Splitting function measurements for Earth's longest period normal modes using recent large earthquakes

2011 ◽  
Vol 38 (4) ◽  
pp. n/a-n/a ◽  
Author(s):  
Arwen Deuss ◽  
Jeroen Ritsema ◽  
Hendrik van Heijst
Keyword(s):  
Normal Modes ◽  
Splitting Function ◽  
Large Earthquakes

scholarly journals Ionospheric Disturbances Observed Following the Ridgecrest Earthquake of 4 July 2019 in California, USA

2022 ◽  
Vol 14 (1) ◽  
pp. 188
Author(s):  
Saul A. Sanchez ◽  
Esfhan A. Kherani ◽  
Elvira Astafyeva ◽  
Eurico R. de Paula
Keyword(s):  
Spectral Characteristics ◽  
Normal Modes ◽  
Electron Content ◽  
Ionospheric Disturbances ◽  
Ground Displacement ◽  
Total Electron ◽  
Resonance Modes ◽  
Seismic Origin ◽  
Threshold Criteria ◽  
Large Earthquakes

Earthquakes are known to generate disturbances in the ionosphere. Such disturbances, referred to as co-seismic ionospheric disturbances, or ionoquakes, were previously reported for large earthquakes with magnitudes Mw≥ 6.6. This paper reports ionoquakes associated with the Ridgecrest earthquakes of magnitude (Mw=6.4), that occurred on 4 July 2019 in California, USA. The ionoquakes manifested in total electron content (TEC) in the form of traveling ionospheric disturbances (TIDs) within 1 h from the mainshock onset. These seismic-origin TIDs have unique wave characteristics that distinguish them from TIDs of non-seismic origin arising from a moderate geomagnetic activity on the same day. Moreover, in the space-time domain of the detection of seismic-origin TIDs, TIDs are absent on the day before and day after the earthquake day. Their spectral characteristics relate them to the Earth’s normal modes and atmospheric resonance modes. We found the ground velocity associated with the mainshock, rather than the ground displacement, satisfies the threshold criteria for detectable ionoquakes in TEC measurements. Numerical simulation suggested that the coupled seismo–atmosphere–ionosphere (SAI) dynamics energized by the atmospheric waves are responsible for the generation of ionoquakes. This study’s findings demonstrate the potential of using TEC measurement to detect the ionospheric counterparts of moderate earthquakes.

FrosPy: A Modular Python Toolbox for Normal Mode Seismology

2022 ◽  
Author(s):  
Simon Schneider ◽  
Sujania Talavera-Soza ◽  
Lisanne Jagt ◽  
Arwen Deuss
Keyword(s):  
Normal Mode ◽  
Free Oscillation ◽  
Large Time ◽  
Reference Model ◽  
Normal Modes ◽  
Earth Model ◽  
Splitting Function ◽  
Quality Factor Q ◽  
Earth’S Free Oscillation ◽  
Q Values

Abstract We present free oscillations Python (FrosPy), a modular Python toolbox for normal mode seismology, incorporating several Python core classes that can easily be used and be included in larger Python programs. FrosPy is freely available and open source online. It provides tools to facilitate pre- and postprocessing of seismic normal mode spectra, including editing large time series and plotting spectra in the frequency domain. It also contains a comprehensive database of center frequencies and quality factor (Q) values based on 1D reference model preliminary reference Earth model for all normal modes up to 10 mHz and a collection of published measurements of center frequencies, Q values, and splitting function (or structure) coefficients. FrosPy provides the tools to visualize and convert different formats of splitting function coefficients and plot these as maps. By giving the means of using and comparing normal mode spectra and splitting function measurements, FrosPy also aims to encourage seismologists and geophysicists to learn about normal mode seismology and the study of the Earth’s free oscillation spectra and to incorporate them into their own research or use them for educational purposes.

Global observations of 3D mantle attenuation using normal modes 

2021 ◽  
Author(s):  
Sujania Talavera-Soza ◽  
Arwen Deuss
Keyword(s):  
Upper Mantle ◽  
Lower Mantle ◽  
Mantle Convection ◽  
Velocity Structure ◽  
3D Structure ◽  
Normal Modes ◽  
Seismic Attenuation ◽  
Body Waves ◽  
Splitting Function ◽  
Thermal Origin

<div> <div> <div> <p>Seismic tomographic models based solely on wave velocities are unable to distinguish between a temperature or compositional origin for Earth’s 3D structure variations, such as the Large Low Shear Velocity Provinces (LLSVPs) beneath the lower mantle of Africa and the Pacific. Seismic attenuation or damping is able able to provide additional information that may help to unravel the origin of the LLSVPs, which is fundamental to understand mantle convection evolution. For example, a thermal origin for the LLSVPs will point to them being short-lived anomalies, whereas a compositional origin will point to them being long-lived, forming mantle 'anchors' and influencing the pattern of mantle convection for a large part of Earth’s history. Seismic attenuation is able to make that distinction, because it is directly sensitive to temperature variations. So far, global 3D attenuation models have only been available for the upper mantle, with only two regional body waves studies exploring the lower mantle (Lawrence and Wysession, 2006; Hwang and Ritsema, 2011).<br>Here, we use normal mode data to measure elastic splitting functions (dependent on velocity and density) and anelastic splitting functions (dependent on attenuation). The advantage of normal modes is that they allow us to include focussing and scattering due to the velocity structure without the need for approximations, because we measure the elastic splitting function jointly with the anelastic splitting function. In our measurements for upper mantle sensi- tive modes, we find anti-correlation between the elastic and anelastic splitting functions, suggesting a thermal origin for low velocity spreading ridges, and agreeing with previous studies. On the other hand, for lower mantle sensitive modes, we find correlation, suggesting the averagely attenuating LLSVPs are surrounded by strongly attenuating regions potentially due to the presence of post-perovskite.</p> </div> </div> </div>

A new 3-D mantle density model from recent normal-mode measurements

2021 ◽  
Author(s):  
Rûna van Tent ◽  
Arwen Deuss ◽  
Andreas Fichtner ◽  
Lars Gebraad ◽  
Simon Schneider ◽  
...  
Keyword(s):  
Normal Mode ◽  
Lower Mantle ◽  
Velocity Structure ◽  
Normal Modes ◽  
Shear Velocity ◽  
Boundary Region ◽  
Splitting Function ◽  
The Pacific ◽  
Compositional Variations ◽  
Body Tides

<p>Constraints on the 3-D density structure of Earth’s mantle provide important insights into the nature of seismically observed features, such as the Large Low Shear Velocity Provinces (LLSVPs) in the lower mantle under Africa and the Pacific. The only seismic data directly sensitive to density variations throughout the entire mantle are normal modes: whole Earth oscillations that are induced by large earthquakes (M<sub>w</sub> > 7.5). However, their sensitivity to density is weak compared to the sensitivity to velocity and different studies have presented conflicting density models of the lower mantle. For example, Ishii & Tromp (1999) and Trampert et al. (2004) have found that the LLSVPs have a larger density than the surrounding mantle, while Koelemeijer et al. (2017) used additional Stoneley-mode observations, which are particularly sensitive to the core-mantle boundary region, to show that the LLSVPs have a lower density. Recently, Lau et al. (2017) have used tidal tomography to show that Earth's body tides prefer dense LLSVPs.</p><p>A large number of new normal-mode splitting function measurements has become available since the last density models of the entire mantle were published. Here, we show the models from our inversion of these recent data and compare our results to previous studies. We find areas of high as well as low density at the base of the LLSVPs and we find that inside the LLSVPs density varies on a smaller scale than velocity, indicating the presence of compositionally distinct material. In fact, we find low correlations between the density and velocity structure throughout the entire mantle, revealing that compositional variations are required at all depths inside the mantle.</p>

scholarly journals A new catalogue of toroidal-mode overtone splitting function measurements

2020 ◽  
Author(s):  
Simon Schneider ◽  
Arwen Deuss
Keyword(s):  
Normal Mode ◽  
Large Scale ◽  
Velocity Structure ◽  
Normal Modes ◽  
Splitting Function ◽  
Data Set ◽  
Toroidal Mode ◽  
Function Coefficient ◽  
Fiji Island ◽  
Shear Wave Velocity Structure

Abstract Spectra of whole Earth oscillations or normal modes provide important constraints on Earth’s large scale structure. The most convenient way to include normal mode constraints in global tomographic models is by using splitting functions or structure coefficients, which describe how the frequency of a specific mode varies regionally. Splitting functions constrain 3D variations in velocity, density structure and boundary topography. They may also constrain anisotropy, especially when combining information from spheroidal modes, which are mainly sensitive to P-SV structure, with toroidal modes, mainly sensitive to SH structure. Spheroidal modes have been measured extensively, but toroidal modes have proven to be much more difficult and as a result only a limited number of toroidal modes have been measured so far. Here we expand the splitting function studies by Resovsky and Ritzwoller (1998) and Deuss et al. (2013), by focusing specifically on toroidal mode overtone observations. We present splitting function measurements for 19 self-coupled toroidal modes of which 13 modes have not been measured before. They are derived from radial and transverse horizontal component normal mode spectra up to 5 mHz for 91 events with MW ≥ 7.4 from the years 1983-2018. Our data include the Tohoku event of 2011 (9.1MW), the Okhotsk event of 2013 (8.3MW) and the Fiji Island event from 2018 (8.2MW). Our measurements provide new constraints on upper and lower mantle shear wave velocity structure and in combination with existing spheroidal mode measurements can be used in future inversions for anisotropic mantle structure. Our new splitting function coefficient data set will be available online.

Filtering methods for finite-time normal modes and atmospheric error growth

2000 ◽  
Vol 42 ◽  
pp. 1482
Author(s):  
Mozheng Wei ◽  
Jorgen S. Frederiksen ◽  
Steve Kepert
Keyword(s):  
Finite Time ◽  
Normal Modes ◽  
Error Growth

Gravitational Waves

2018 ◽  
Author(s):  
Michele Maggiore
Keyword(s):  
Black Hole ◽  
Perturbation Theory ◽  
Gravitational Waves ◽  
Transfer Functions ◽  
Normal Modes ◽  
Cosmological Perturbation ◽  
Tests Of General Relativity ◽  
Pulsar Timing ◽  
Tensor Perturbations ◽  
Stochastic Backgrounds

A comprehensive and detailed account of the physics of gravitational waves and their role in astrophysics and cosmology. The part on astrophysical sources of gravitational waves includes chapters on GWs from supernovae, neutron stars (neutron star normal modes, CFS instability, r-modes), black-hole perturbation theory (Regge-Wheeler and Zerilli equations, Teukoslky equation for rotating BHs, quasi-normal modes) coalescing compact binaries (effective one-body formalism, numerical relativity), discovery of gravitational waves at the advanced LIGO interferometers (discoveries of GW150914, GW151226, tests of general relativity, astrophysical implications), supermassive black holes (supermassive black-hole binaries, EMRI, relevance for LISA and pulsar timing arrays). The part on gravitational waves and cosmology include discussions of FRW cosmology, cosmological perturbation theory (helicity decomposition, scalar and tensor perturbations, Bardeen variables, power spectra, transfer functions for scalar and tensor modes), the effects of GWs on the Cosmic Microwave Background (ISW effect, CMB polarization, E and B modes), inflation (amplification of vacuum fluctuations, quantum fields in curved space, generation of scalar and tensor perturbations, Mukhanov-Sasaki equation,reheating, preheating), stochastic backgrounds of cosmological origin (phase transitions, cosmic strings, alternatives to inflation, bounds on primordial GWs) and search of stochastic backgrounds with Pulsar Timing Arrays (PTA).

Triatomic molecules

2018 ◽  
Author(s):  
John H. D. Eland ◽  
Raimund Feifel
Keyword(s):  
Degrees Of Freedom ◽  
Normal Modes ◽  
Electronic States ◽  
Triatomic Molecules ◽  
Doubly Charged Ions ◽  
Spectral Bands ◽  
Valence Electrons ◽  
Doubly Charged ◽  
Charged Ions ◽  
Double Ionisation

Double ionisation of the triatomic molecules presented in this chapter shows an added degree of complexity. Besides potentially having many more electrons, they have three vibrational degrees of freedom (three normal modes) instead of the single one in a diatomic molecule. For asymmetric and bent triatomic molecules multiple modes can be excited, so the spectral bands may be congested in all forms of electronic spectra, including double ionisation. Double photoionisation spectra of H2O, H2S, HCN, CO2, N2O, OCS, CS2, BrCN, ICN, HgCl2, NO2, and SO2 are presented with analysis to identify the electronic states of the doubly charged ions. The order of the molecules in this chapter is set first by the number of valence electrons, then by the molecular weight.

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