NEW_Accomplishments.indd - IRIS

SURFACE OF THE EARTH: GLOBAL STUDIES
2006 IRIS 5-YEAR PROPOSAL
The Reflections Under the Scottish Highlands (RUSH) EXPERIMENT:
Mapping Fine-Scale Heterogeneities within the Continental Mantle Lithosphere
Beneath Scotland, Combining Active- and Passive-Source Seismology
Eugenio Asencio • University of Puerto Rico
James H. Knapp, Thomas J. Owens • University of South Carolina
George Helffrich • University of Bristol
The structure and evolution of the continental mantle lithosphere constitute a fundamental frontier of continental tectonics.
Developments in the field of seismology over the last decade in recording technology, data volume, and analysis techniques have led
to a potentially powerful capability to integrate active- and passive-source seismology to image upper mantle structure across a spectrum
of observational scales. Northern Scotland offers the opportunity to explore this integrated seismological approach due to the
variety of observations suggesting fine-scale upper mantle layering. Toward this end, we tapped the BIRPS database of upper mantle
reflections identified on near-vertical deep seismic reflection profiles and we deployed 24-broadband PASSSCAL seismographs during
the summer of 2001 (Asencio et. al., 2001, 2003) across the Scottish Highlands (Figure 1).
We analyze new observational evidence for seismic velocity discontinuities in teleseismic receiver functions in comparison
to well-documented discontinuities observed in marine reflection profiles and wide-angle reflection-refraction profiles in northern
Scotland. Our study establishes the viability of mapping small amplitude P-to-S (Ps) converted phase arrivals from the upper
mantle generated in the P-wave coda of teleseismic earthquakes using well-known receiver function methods (Figure 2).
This investigation (Asencio, 2003) represents the joint use of two different approaches to seismic mapping of lithospheric structures
and addresses the utility of correlating active- and passive-source seismology for understanding the tectonic significance and
evolution of upper mantle structures. Application of this combined analysis provides some insight into the origin and lateral extent of
upper mantle velocity discontinuities beneath Scotland.
Figure 2. Correlation of radial component of
receiver functions (as a function of event back
azimuth) at: (A) ORE station with major reflectors
on DRUM deep seismic reflection profile:
(B) RRR station with major reflectors on GRID-9
deep seismic reflection profile. Vertical scale is
two-way travel time in seconds.
Figure 1. The Reflections Under the
Scottish Highland (RUSH) Experiment,
showing: (1) PASSCAL broadband stations
(blue circles); (2) location of deep
seismic reflection profiles (the DRUM
and GRID-9 profiles shown in bold
red); and, (3) permanent BGS 3-comp.
stations (red stars).
Asencio, E., Imaging Lithospheric Structure in Northern Scotland
and the South Caspian basin, Ph.D. Dissertation, University of South
Carolina, Columbia, U.S, 2003.
Asencio, E., Knapp, J.H., Owens, T.J., and Helffrich, G., Mapping
fine-scale heterogeneities within the continental mantle lithosphere
beneath Scotland: Combining active and passive-source seismology,
Geology, 31, pp. 447-480, 2003.
Asencio, E., Knapp, J.H., Owens, T.J., and Helffrich, G., The Reflection
Under the Scottish Highlands
(RUSH-II) Experiment: Broadband
definition of upper mantle structures:
Eos Trans. AGU, 82, Fall Meet.
Suppl., Abstract S12D-0644, 2001.
This work was funded in part by
grant EAR0074002 from the US
National Science Foundation, grant
GR9/04304 from the UK Natural
Environment Research Council.
We would like to thank the NERC
Geophysical Equipment Pool and
PASSCAL for providing the equipment
and logistical support in the
field and the IRIS Data Management
Center and the British Geological
Survey for making available the data
through their automatic data server.
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