Rotational Motions in Seismology: Theory, Observation, Simulation

Cochard, Alain; Igel, Heiner; Schuberth, Bernhard S. A.; Suryanto, Wiwit; Velikoseltsev, A.; Schreiber, Ulrich; Wassermann, Joachim; Scherbaum, Frank; Vollmer, Daniel

doi:10.1007/3-540-31337-0_30

Cited by 102 publications

(58 citation statements)

References 27 publications

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“…These have two major advantages for applications in seismic studies compared to the other seismometers discussed above, since they measure absolute rotation with respect to the local universe, and they do not depend on accelerated masses. In particular, this last property ensures an extremely wide dynamic range of operation, from a few 10 −6 Hz for geophysical signals up to more than 10 Hz, as obtained from regional earthquakes [83]. Since the G-ring laser is at present the system with the best signal-to-noise performance, its parameters are included in Table 3 for comparison with other optical rotational seismometers.…”

Section: Rotational Seismometers For Direct Measurement Of Rotationmentioning

confidence: 99%

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Review of the Usefulness of Various Rotational Seismometers with Laboratory Results of Fibre-Optic Ones Tested for Engineering Applications

Jaroszewicz

Kurzych

Krajewski

et al. 2016

Sensors

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Starting with descriptions of rotational seismology, areas of interest and historical field measurements, the fundamental requirements for rotational seismometers for seismological and engineering application are formulated. On the above basis, a review of all existing rotational seismometers is presented with a description of the principles of their operation as well as possibilities to fulfill formulated requirements. This review includes mechanical, acoustical, electrochemical and optical devices and shows that the last of these types are the most promising. It is shown that optical rotational seismometer based on the ring-laser gyroscope concept is the best for seismological applications, whereas systems based on fiber-optic gyroscopes demonstrate parameters which are also required for engineering applications. Laboratory results of the Fibre-Optic System for Rotational Events & Phenomena Monitoring using a small 1-D shaking table modified to generate rotational excitations are presented. The harmonic and time-history tests demonstrate its usefulness for recording rotational motions with rates up to 0.25 rad/s.

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Section: Rotational Seismometers For Direct Measurement Of Rotationmentioning

confidence: 99%

“…For the above reasons, they generally fulfil only the S1, E1 and S4 requirements. However, for the last two decades they have been sufficient for practical use in the detection of rotation events in both strong and weak earthquakes [83,85,86,87]. …”

Section: Rotational Seismometers For Direct Measurement Of Rotationmentioning

confidence: 99%

Review of the Usefulness of Various Rotational Seismometers with Laboratory Results of Fibre-Optic Ones Tested for Engineering Applications

Jaroszewicz

Kurzych

Krajewski

et al. 2016

Sensors

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“…Several authors report rotations excited by teleseismic waves ͑e.g., Pancha et al, 2000;Igel et al, 2005Igel et al, , 2007Cochard et al, 2006͒. Reports of rotational ground motions recorded in the nearsource region can be found in Nigbor ͑1994͒, Takeo Seismically induced rotational ground motions contain information about the structure of the earth.…”

Section: Introductionmentioning

confidence: 95%

Inferring earth structure from combined measurements of rotational and translational ground motions

2009

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We introduce a novel variant of seismic tomography that is based on colocated measurements of rotational and translational ground motions. Our aim is to assess whether rotations may be incorporated successfully into seismic inverse problems to produce better resolved and more realistic tomographic images. Our methodology is based on the definition of apparent S-wave speed as the ratio of rms velocity and rotation amplitudes. The principal advantages of this definition are that ͑1͒ no traveltimes measurements are needed and ͑2͒ the apparent S-wave speed is independent of source magnitude and source timing. We derive finite-frequency kernels for apparent S-wave speed by using a combination of the adjoint method and ray approximation. The properties of these kernels as a function of frequency bandwidth can be illustrated along with their usefulness for seismic tomography. In multifrequency synthetic inversions, we consider local crosshole tomography and regional-scale earthquake tomography.Our results indicate that S-wave speed variations can be retrieved accurately from colocated rotation and translation measurements, suggesting that our methodology is a promising extension of conventional seismic tomography. Further, apparent S-wave speed can be used to increase vertical resolution in teleseismic tomography for local structures.

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“…Theoretical studies, for example, by Cochard et al (2), indicate that the observations of seismic rotational motions will provide important new information pertaining to the Earth sciences, complementary to those obtained from the observations of the translational motions of the Earth surface using conventional seismometers. They note that combining the observation of rotational motion with the concomitant translational motion yields wave-field properties such as phase velocities and the direction of propagation.…”

mentioning

confidence: 99%

“…Accordingly, Cochard et al (2) have emphasized that recording even small, rotational motions with low potential for causing damage would be useful, especially because of possible cross-couplings between rotational motions and tilt motions (Todorovska and Trifunac,ref. 4).…”

mentioning

confidence: 99%

An instrument for direct observations of seismic and normal-mode rotational oscillations of the Earth

Cowsik¹

2007

Proc. Natl. Acad. Sci. U.S.A.

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The rotations around the vertical axis associated with the normal mode oscillations of the Earth and those induced by the seismic and other disturbances have been very difficult to observe directly. Such observations will provide additional information for 3D modeling of the Earth and for understanding earthquakes and other underground explosions. In this paper, we describe the design of an instrument capable of measuring the rotational motions associated with the seismic oscillations of the Earth, including the lowest frequency normal mode at Ϸ 3.7 ؋ 10 ؊4 Hz. The instrument consists of a torsion balance with a natural frequency of 0 Ϸ 1.6 ؋ 10 ؊4 Hz, which is observed by an autocollimating optical lever of high angular resolution and dynamic range. Thermal noise limits the sensitivity of the apparatus to amplitudes of Ϸ 1.5 ؋ 10 ؊9 rad at the lowest frequency normal mode and the sensitivity improves as ؊3/2 with increasing frequency. Further improvements in sensitivity by about two orders of magnitude may be achieved by operating the balance at cryogenic temperatures. Alternatively, the instrument can be made more robust with a reduced sensitivity by increasing 0 to Ϸ10 ؊2 Hz. This instrument thus complements the ongoing effort by Igel and others to study rotational motions using ring laser gyroscopes and constitutes a positive response to the clarion call for T orsional oscillations of the Earth, sometimes called torroidal oscillations were predicted in the 19th century and have been calculated with increasing precision during the recent decades. The lowest of these modes involve the oscillations of the entire mantle and have periods of Ϸ3,000 s. Careful measurement of these oscillations is of considerable importance in understanding the Earth and the mechanism of earthquakes. The rotations associated with the normal modes of the Earth have not been directly observed with the present-day instruments. Seismological studies have been mostly responsible for our understanding of the nature and dynamics of the interior of the Earth, with additional information coming from other channels such as paleomagnetism, VLBI, and GPS. At present, the seismological studies are essentially limited to monitoring global and local wave fields at various frequencies, measuring only the three components of the translational velocity of ground displacement and in some cases directly the strains. The Fourier transform of the horizontal translations yields the frequency spectrum of these oscillations, and their correspondence with theoretical calculations carried out with the PREM model of Dziewonski and Anderson allows us to identify the frequencies and Q values associated with the rotational oscillations of the Earth's mantle. In a unique effort, Igel et al. (1) have been able to detect the rotational motions induced by the M8.1 Tokachi-Oki earthquake at frequencies of the order of 30-60 mHz, using ring laser gyroscopes.Theoretical studies, for example, by Cochard et al. (2), indicate that the observations of seismic rotational mot...

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Rotational Motions in Seismology: Theory, Observation, Simulation

Cited by 102 publications

References 27 publications

Review of the Usefulness of Various Rotational Seismometers with Laboratory Results of Fibre-Optic Ones Tested for Engineering Applications

Review of the Usefulness of Various Rotational Seismometers with Laboratory Results of Fibre-Optic Ones Tested for Engineering Applications

Inferring earth structure from combined measurements of rotational and translational ground motions

An instrument for direct observations of seismic and normal-mode rotational oscillations of the Earth

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