Micropolar modelling of rotational waves in seismology

• Published in: Geophysical journal international Vol. 210; no. 2; pp. 1021 - 1046
• Main Authors: Abreu, Rafael, Kamm, Jochen, Reiß, Anne-Sophie
• Format: Journal Article
• Language: English
• Published: Oxford University Press 01.08.2017
• Subjects: Computational seismology; Microstructures; Theoretical seismology; Wave propagation; Theoretical seismology; Wave propagation; Microstructures; Computational seismology
• ISSN: 0956-540X; 1365-246X; 1365-246X
• DOI: 10.1093/gji/ggx211

Abstract In this contribution we study elastic wave propagation via the introduction of the micropolar theory. As a generalization of a classical linear elastic medium, a micropolar medium allows each particle to have intrinsic rotational degrees of freedom (spin). We perform numerical experiments using the Pseudospectral method. We find analytical harmonic micropolar solutions for different problem configurations, which result in waveform differences between the classical linear elastic and micropolar media. In contrast to linear elastic media, wave propagation in micropolar media is dispersive. We study how the spin waveform depends on the micropolar elastic parameters and frequency content of the simulation. The micropolar effect on numerical seismograms has a direct implication on the phase, amplitude and arrival time. For frequencies lower than the cut-off frequency, the spin waveform has the same amplitude as the macrorotation field. For frequencies higher than the cut-off frequency, the amplitude of the spin waveform decreases with increasing frequency, so that then it is no longer comparable to the amplitude of macroscopic rotations. When both frequencies are equal there is no wave propagation. This work attempts to clarify the theory of micropolar media for its applications in seismology. We argue that micropolar theory should be further investigated for its potential uses in seismology to, for example, describe energy dissipation, seismograms recorded with rotational seismometers and rupture processes.