Tutorial on rotational seismology and its applications in exploration geophysics

Geophysics ◽  
2017 ◽  
Vol 82 (5) ◽  
pp. W17-W30 ◽  
Author(s):  
Zhenhua Li ◽  
Mirko van der Baan
Keyword(s):  
Ground Motion ◽  
Rotational Motion ◽  
Moment Tensor ◽  
Spatial Gradient ◽  
Rotational Seismology ◽  
Rotational Ground Motion ◽  
Reflection Seismic ◽  
Full Analysis ◽  
Pressure Changes ◽  
Wavefield Extrapolation

Traditionally, seismological interpretations are based on the measurement of only translational motions, such as particle displacement, velocity, and/or acceleration, possibly combined with pressure changes; yet theory indicates that rotational motions should also be observed for a complete description of all ground motions. The recent and ongoing development of rotational sensors renders a full analysis of the translational and rotational ground motion possible. We have developed the basic mathematical theory related to rotational motion. And we also evaluated several instruments used to directly measure the rotational ground motion, which may be applicable for exploration geophysics. Finally, we made several applications of rotational motion in exploration geophysics, namely, (1) P- and S-wavefield separation, (2) wavefield reconstruction, (3) ground-roll removal, (4) microseismic event localization and reflection seismic migration by wavefield extrapolation, and (5) moment tensor inversion. The cited research shows that in particular, the information on the spatial gradient of the wavefield obtained by rotational sensors is beneficial for many purposes. This tutorial is meant to (1) enhance familiarity with the concept of rotational seismology, (2) lead to additional applications, and (3) fast track the continued development of rotational sensors for global and exploration geophysical use.

scholarly journals Seismic moment tensors from synthetic rotational and translational ground motion: Green’s functions in 1-D versus 3-D

2020 ◽  
Vol 223 (1) ◽  
pp. 161-179
Author(s):  
S Donner ◽  
M Mustać ◽  
B Hejrani ◽  
H Tkalčić ◽  
H Igel
Keyword(s):  
Ground Motion ◽  
Seismic Moment ◽  
Structural Model ◽  
Moment Tensor ◽  
Waveform Inversion ◽  
Seismic Moment Tensor ◽  
Tectonic Event ◽  
Moment Tensors ◽  
Rotational Ground Motion ◽  
D Model

SUMMARY Seismic moment tensors are an important tool and input variable for many studies in the geosciences. The theory behind the determination of moment tensors is well established. They are routinely and (semi-) automatically calculated on a global scale. However, on regional and local scales, there are still several difficulties hampering the reliable retrieval of the full seismic moment tensor. In an earlier study, we showed that the waveform inversion for seismic moment tensors can benefit significantly when incorporating rotational ground motion in addition to the commonly used translational ground motion. In this study, we test, what is the best processing strategy with respect to the resolvability of the seismic moment tensor components: inverting three-component data with Green’s functions (GFs) based on a 3-D structural model, six-component data with GFs based on a 1-D model, or unleashing the full force of six-component data and GFs based on a 3-D model? As a reference case, we use the inversion based on three-component data and 1-D structure, which has been the most common practice in waveform inversion for moment tensors so far. Building on the same Bayesian approach as in our previous study, we invert synthetic waveforms for two test cases from the Korean Peninsula: one is the 2013 nuclear test of the Democratic People’s Republic of Korea and the other is an Mw  5.4 tectonic event of 2016 in the Republic of Korea using waveform data recorded on stations in Korea, China and Japan. For the Korean Peninsula, a very detailed 3-D velocity model is available. We show that for the tectonic event both, the 3-D structural model and the rotational ground motion, contribute strongly to the improved resolution of the seismic moment tensor. The higher the frequencies used for inversion, the higher is the influence of rotational ground motions. This is an important effect to consider when inverting waveforms from smaller magnitude events. The explosive source benefits more from the 3-D structural model than from the rotational ground motion. Nevertheless, the rotational ground motion can help to better constraint the isotropic part of the source in the higher frequency range.

scholarly journals Rotational Ground Motion Measurements for Regional Seismic Moment Tensors: a Review

2021 ◽  
Author(s):  
Stefanie Donner
Keyword(s):  
Ground Motion ◽  
Seismic Moment ◽  
Spatial Scales ◽  
Moment Tensor ◽  
Waveform Inversion ◽  
Seismic Source ◽  
Seismic Moment Tensor ◽  
Moment Tensors ◽  
Rotational Ground Motion ◽  
Motion Measurements

Seismic moment tensors are an important tool in geosciences on all spatial scales and for a broad range of applications. The basic underlying theory is established since decades. However, various factors influence the reliability of the inversion result, several of them are mutually dependent. Hence, a reliable retrieval of seismic moment tensors is still hampered in many cases, especially at regional event-receiver distances.To sample the entire wavefield due to a seismic source we need six components: three translational and three rotational ones. Up to now, only translational ground motion recordings were used for moment tensor retrieval, missing out valuable information. Using rotational in addition to the classical translational ground motions during waveform inversion for moment tensors mainly adds information on the vertical displacement gradient to the inversion problem. Furthermore, having available six instead of only three components per receiver location provides additional constraints on the sampling of the radiation pattern. As a result, the moment tensor components are resolved with higher precision and accuracy, even when the number of recording receivers is considerably reduced. Especially, components with a dependence to depth as well as the centroid depth can benefit significantly from additional rotational ground motion. Up to the time of writing this review only a few studies are published on the topic. Here, I summarise their findings and provide an overview over the possible capabilities of including rotational ground motion measurements to waveform inversion for seismic moment tensor retrieval.

scholarly journals Corrigendum: 6-C polarization analysis using point-measurements of translational and rotational ground-motion: theory and applications

2018 ◽  
Vol 214 (2) ◽  
pp. 1466-1466
Author(s):  
David Sollberger ◽  
Stewart A Greenhalgh ◽  
Cedric Schmelzbach ◽  
Cédéric Van Renterghem ◽  
Johan O A Robertsson
Keyword(s):  
Ground Motion ◽  
Polarization Analysis ◽  
Rotational Ground Motion

The seismic broad-band antenna of the Low Noise Underground Laboratory (LSBB, Rustrel, France): a tool for measuring the rotation ground motion.

2020 ◽  
Author(s):  
Olivier Sèbe ◽  
Stéphane Gaffet ◽  
Roxanne Rusch ◽  
Jean-Baptiste Decitre ◽  
Charly Lallemand ◽  
...  
Keyword(s):  
Ground Motion ◽  
Ground Motions ◽  
Broad Band ◽  
Low Noise ◽  
Underground Laboratory ◽  
Finite Difference Approximation ◽  
Difference Approximation ◽  
Spatial Gradient ◽  
Small Aperture ◽  
Seismic Wavefield

<p>I<span>n the last 20 years, seismologists have recognized that a better sensing of the seismic wavefield is obtained by considering the rotational ground motions in addition to the translation measurements usually provided by seismometers. Even though recent technological developments have resulted in new portable rotation sensors with a sensitivity and a bandwidth suited to seismological applications requirements, the ground rotations have for a long time been estimated indirectly by dense seismic arrays.</span></p><p><span>The Low Noise Underground Laboratory (LSBB) includes a dense 3D seismic antenna composed of 6 STS2 broad-band seismometers since March 2005. From 2016, this array has been upgraded by the installation of about 10 new seismometers at the surface and inside the galleries of the laboratory. Thanks to these dense and small aperture seismic networks, the vertical and horizontal rotations of the ground motion have been estimated by finite difference approximation of the spatial derivatives of the local ground motions. These measurements provide the opportunity to conduct six degree of freedom (6DOF) analysis (3C translations and 3C rotations) to find out the direction of the wave propagation and to estimate the seismic wave local phase velocity. </span></p><p><span>The performance of this seismic array in deriving the local spatial gradient of the seismic wavefield, as well as the rotation tensor, will be illustrated by several selected seismic records such as the 2016 central Italy crisis (Amatrice and Norcia events) as well as the recent local Teil earthquake. In addition, the Array Derived Rotations (ADR) from the LSBB antenna are compared with the rotations measured by different kinds of rotation sensors including 2 prototypes of the new BlueSeis3A and a Lily Borehole Tiltmeter.</span></p>

The ROMY project: A 4-component ring laser for geophysics and geodesy

2020 ◽  
Author(s):  
Heiner Igel ◽  
Felix Bernauer ◽  
Joachim Wassermann ◽  
Shihao Yuan ◽  
Andre Gebauer ◽  
...  
Keyword(s):  
Ground Motion ◽  
Ring Laser ◽  
High Sensitivity ◽  
Point Of View ◽  
Small Scale ◽  
Broadband Seismometer ◽  
Rotational Ground Motion ◽  
Noise Characteristics ◽  
The Individual ◽  
Redundant Component

<p>The ROMY ring laser was constructed with 4 non-orthogonal triangular-shaped cavities of 12 m side length in the Geophysical Observatory outside Munich, Germany, in 2016. The large dimensions of the individual rings have the benefit of allowing high sensitivity surpassing in principle the sensitivity of the G-ring at the Fundamentalstation Wettzell. However, the concrete construction of ROMY is geometrically less stable than the G-ring that is built on a rigid Xerodur plate. Each of the four rings has its own Sagnac frequency. The horizontal triangular ring laser at the top of the inverted tetrahedral ROMY structure allows direct comparison of teleseismic signals and noise with the G-ring at a distance of 200km. It also serves as redundant component. In principle, three orthogonal components of rotational ground motion can be obtained by linear combination from any combination of three rings, that - due to the variable Sagnac frequency - have different noise characteristics. We report on the behavior and observations of ROMY from a seismological point of view. It is fair to say that ROMY provides the most accurate direct 3-component rotational ground motion seismic observations to date. In combination with a collocated broadband seismometer as well as a surrounding small-scale seismic array, we analyse regional, teleseismic events, and ocean-generated noise and compare with array-derived rotation.</p>

Design for seismic torsional forces

1984 ◽  
Vol 11 (2) ◽  
pp. 150-163 ◽  
Author(s):  
J. L. Humar
Keyword(s):  
Ground Motion ◽  
Analytical Study ◽  
Critical Evaluation ◽  
Building Code ◽  
Rotational Ground Motion ◽  
Building Model ◽  
Design Basis ◽  
Building Models ◽  
Adequate Design ◽  
Code Provisions

An analytical study of the responses of a single storey and a multistorey building model to a combined translational and rotational ground motion is presented. The models, which are assumed to be elastic, are eccentric about one plan direction but are symmetric about the perpendicular direction. The ground excitations are represented by idealized spectra.A critical evaluation is made of the torsion provisions of the National Building Code of Canada. It is shown that the code provisions, while not necessarily nonconservative, are somewhat difficult to apply for multistorey buildings. An alternative provision for design eccentricity is proposed. The forces obtained by the use of the proposed method are compared with the analytical results of single storey and multistorey building models and are shown to provide an adequate design basis.

scholarly journals Long-Period Ground Motion Simulation Based on Three-dimensional Centroid Moment Tensor Inversion Solutions in the Kanto Region, Japan

2020 ◽  
Author(s):  
Shunsuke Takemura ◽  
Kazuo Yoshimoto ◽  
Katsuhiko Shiomi
Keyword(s):  
Ground Motion ◽  
Ground Motions ◽  
Moment Tensor ◽  
Three Dimensional ◽  
Centroid Moment Tensor ◽  
Velocity Models ◽  
Long Period ◽  
Ground Motion Simulations ◽  
Kanto Basin ◽  
Long Period Ground Motion

Abstract We conducted centroid moment tensor (CMT) inversions of moderate (Mw 4.5–6.5) earthquakes in the Kanto region, Japan, using a local three-dimensional (3D) model. We then investigated the effects of our 3D CMT solutions on long-period ground motion simulations. Grid search CMT inversions were conducted using displacement seismograms for periods of 25–100 s. By comparing our 3D CMT solutions with those from the local one-dimensional (1D) catalog, we found that our 3D CMT inversion systematically provides magnitudes smaller than those in the 1D catalog. The Mw differences between 3D and 1D catalogs tend to be significant for earthquakes within the oceanic slab. By comparing ground motion simulations between 1D and 3D velocity models, we confirmed that observed Mw differences could be explained by differences in the rigidity structures around the source regions between 3D and 1D velocity models. The 3D velocity structures (especially oceanic crust and mantle) are important for estimating seismic moments in intraslab earthquakes. The seismic moments directly affect the amplitudes of ground motions. Thus, 3D CMT solutions are essential for the precise forward and inverse modeling of long-period ground motion. We also conducted long-period ground motion simulations using our 3D CMT solutions to evaluate reproducibility of long-period ground motions at stations within the Kanto Basin. The simulations of our 3D CMT inversion well-reproduced observed ground motions for periods longer than 10 s, even at stations within the Kanto Basin.

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