Upper mantle structure beneath central Eurasia using a source array of nuclear explosions and waveforms at regional distances

Journal Article · Thu Sep 10 04:00:00 EDT 1992 · Journal of Geophysical Research

DOI:https://doi.org/10.1029/92JB01205· OSTI ID:70541

Goldstein, P; Walter, W R; Zandt, G ^[1]

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1. Lawrence Livermore National Lab., CA (United States)

The authors have observed consistent broadband, regional, three-component P waveforms from a set of 11 explosions that occurred at the former Soviet test site in Kazakhstan during 1988 and 1989 and have modeled most of the prominent features in these waveforms to determine upper mantle structure beneath central Eurasia. Using a subset of events as a source array, they have identified four consistent arrivals during the first 15 s of P waves recorded at the Soviet/Incorporated Research Institutions for Seismology (IRIS) stations Arti (ARU) (d {approx} 1500 km) and Garm (GAR) (d {approx} 1380 km). These arrivals show consistent variations in frequency content, relative timing, and amplitudes from event to event despite a range in source magnitude (m{sub b}) between 4.9 and 6.1. They have also identified consistent features in P waveforms of these events recorded at Obninsk (OBN) (d {approx} 2880 km). The authors argue that most of the prominent features in these waveforms can be explained by reflections at or refractions near discontinuities or large velocity gradients in the upper mantle. They show that a model with discontinuities of approximately 3.0% and 6.5% near 200 km and 400 km, respectively, produces a better fit to the broadband data at ARU and GAR than previous models for this region. This model also produces a good match to waveforms recorded at OBN and NORESS, however, this model is not unique. For example, the authors show that it is also possible to produce similar waveforms by replacing the 200 km discontinuity with a large, notch shaped, low velocity zone between approximately 100 and 140 km. Based on reflectivity synthetics, they suggest that additional data, especially from distances less than 1000 km, should indicate which of these models is more accurate. Comparison of these results with other upper mantle studies shows that the central Eurasian upper mantle is similar to the upper mantle of the central and eastern USA. 34 refs., 18 figs., 3 tabs.

• Sponsoring Organization: USDOE
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 70541
• Journal Information: Journal of Geophysical Research, Journal Name: Journal of Geophysical Research Journal Issue: B10 Vol. 97; ISSN JGREA2; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
EARTH MANTLE
EASTERN EUROPE
SEISMIC P WAVES
STRUCTURAL MODELS
UNDERGROUND EXPLOSIONS