Anne-Sophie Reiß

University of Münster

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Christine Thomas

University of Münster

Jac van Driel

University College London

Björn H. Heyn

University of Oslo

Rafael Abreu

Institut de physique du globe de Paris

Jochen Kamm

Geological Survey of Finland

Thomas Lecocq

Royal Observatory of Belgium

Cooperative Institutions

University of Münster

Centre National de la Recherche Scientifique

University College London

Institut de physique du globe de Paris

Université Paris Cité

Universidad de Oriente

Universidad de Granada

Instituto Andaluz de Ciencias de la Tierra

Geological Survey of Finland

Elektrometall (Czechia)

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Upper mantle seismic discontinuities in the area of the Indian Ocean Geoid Low

EGU General Assembly Conference Abstracts (2017)

Anne-Sophie Reiß Jac van Driel Björn H. Heyn Christine Thomas

Classification of discontinuities

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A hot midmantle anomaly in the area of the Indian Ocean Geoid Low

Geophysical Research Letters (2017)

Anne-Sophie Reiß Christine Thomas Jac van Driel Björn H. Heyn

Abstract We investigate the upper mantle seismic discontinuities at 410 and 660 km depth beneath the Indian Ocean Geoid Low (IOGL). To map the discontinuities' topography, we use differential travel times of PP and SS waves and their precursors. Our final data set consists of 37 events with M w ≥ 5.8, which densely cover our investigation area, also with crossing ray paths. We use array methods to detect the low‐amplitude precursor signals. The best quality data show a deepened 410 km discontinuity in the center of the IOGL as well as a mostly elevated 660 km discontinuity beneath the northern Indian Ocean, which we interpret as a hot anomaly currently residing in the mantle transition zone. We conclude that the largest negative geoid anomaly might be caused by a combined effect of hot material in the midmantle below the innermost IOGL and cold material below 660 km farther south.

Classification of discontinuities

Discontinuity (linguistics)

Anomaly (physics)

10.1002/2017gl073440

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Citations (26)

Using SP precursor waves to detect upper-mantle discontinuities

Geophysical Journal International (2018)

Anne-Sophie Reiß Christine Thomas Thomas Lecocq

We investigate the usability of the converted phase SP and its precursors, which reflect off the underside of upper-mantle seismic discontinuities. In contrast to PP and SS waves, the SP phases do not reflect midway between source and receiver but about three quarters on the great circle path. This leads to extended data coverage, especially in oceanic regions, where usually few receivers are deployed. Due to similar traveltimes and incidence angles, SP is difficult to distinguish from the PS phase. One feature that makes it possible to separate these two waves is their polarization. Therefore, we developed a polarization filter, which allows detecting precursor signals of SP in vespagrams. For this feasibility study, we analysed events from all azimuthal directions with Mw ≥ 5.8 and ranging between 80° and 140° epicentral distance recorded at the western part of the Transportable Array in the United States. Even though this method has several restrictions like limited distance and depth ranges for which the precursor signals are clearly identifiable, this study resulted in 52 events showing signals reflected off the underside of the 410 and/or 660 km discontinuity. Our averaged results show a deepened 410 km discontinuity beneath the Gulf of Alaska, central Alaska and western Canada and a shallower 410 km discontinuity beneath the northern east Pacific Ocean and the coast of Mexico. For the 660 km discontinuity we find fewer reflections. This discontinuity seems to be slightly elevated in central Alaska and beneath the Pacific shore of Mexico. The southern coast of Alaska and parts of Canada show a deepened 660 km discontinuity. These observations agree with previous results of PP-precursors, SS-precursors and receiver function studies. We show that SP precursors are a successful new approach to map upper-mantle seismic discontinuities.

Classification of discontinuities

Discontinuity (linguistics)

Seismogram

10.1093/gji/ggy369

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Citations (3)

Using SP precursor waves to detect upper mantle discontinuities

EGU General Assembly Conference Abstracts (2018)

Anne-Sophie Reiß Christine Thomas

Classification of discontinuities

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Investigation of upper mantle seismic discontinuities beneath the Indian Ocean using array seismology methods

AGUFM (2016)

Jac van Driel Anne-Sophie Reiß Christine Thomas

Classification of discontinuities

Seismic array

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Micropolar modelling of rotational waves in seismology

Geophysical Journal International (2017)

Rafael Abreu Jochen Kamm Anne-Sophie Reiß

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.

Seismogram

Seismometer

Dispersive body waves

10.1093/gji/ggx211

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Citations (21)

Behaviour of mantle transition zone discontinuities beneath the Indian Ocean from PP and SS precursors

EGUGA (2015)

Anne-Sophie Reiß Christine Thomas

Classification of discontinuities

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