TY - JOUR
T1 - Teleseismic Pn arrivals
T2 - Influence of mantle velocity gradient and crustal scattering
AU - Nielsen, L.
AU - Thybo, H.
AU - Morozov, I. B.
AU - Smithson, S. B.
AU - Solodilov, L.
PY - 2003/2
Y1 - 2003/2
N2 - Teleseismic Pn phases with a long, high-amplitude coda, are observed to offsets >3000 km along the Peaceful Nuclear Explosion seismic profiles Quartz and Ruby. For the high-frequency (>5 Hz) part of the Quartz data, which is shown here, coda lengths of more than 10 s can be visually observed in the seismic sections. We interpret the teleseismic Pn arrivals as multiple sub-Moho refractions (whispering-gallery phases), which travel over large distances due to a positive upper-mantle velocity gradient. The coda of these arrivals is explained by lower crustal scattering of the whispering-gallery phases from the mantle. The modelling is based on calculation of reflectivity and 2-D visco-elastic finite-difference synthetic seismograms. Our models are in agreement with other deep seismic data from continental areas, which typically show a reflective lower crust and an almost transparent uppermost mantle. The lower crustal heterogeneity is described by von Karman distribution with a standard deviation of 0.5 km s-1 for the P-wave velocity and correlation lengths of 2.4 km (horizontally) and 0.6 km (vertically). The positive vertical upper-mantle velocity gradient of ∼0.004 km s-1 km-1, which is characteristic for profile Quartz, forms a waveguide which gives rise to the teleseismic Pn. It is not necessary to include upper-mantle heterogeneity in order to explain the characteristics of this arrival.
AB - Teleseismic Pn phases with a long, high-amplitude coda, are observed to offsets >3000 km along the Peaceful Nuclear Explosion seismic profiles Quartz and Ruby. For the high-frequency (>5 Hz) part of the Quartz data, which is shown here, coda lengths of more than 10 s can be visually observed in the seismic sections. We interpret the teleseismic Pn arrivals as multiple sub-Moho refractions (whispering-gallery phases), which travel over large distances due to a positive upper-mantle velocity gradient. The coda of these arrivals is explained by lower crustal scattering of the whispering-gallery phases from the mantle. The modelling is based on calculation of reflectivity and 2-D visco-elastic finite-difference synthetic seismograms. Our models are in agreement with other deep seismic data from continental areas, which typically show a reflective lower crust and an almost transparent uppermost mantle. The lower crustal heterogeneity is described by von Karman distribution with a standard deviation of 0.5 km s-1 for the P-wave velocity and correlation lengths of 2.4 km (horizontally) and 0.6 km (vertically). The positive vertical upper-mantle velocity gradient of ∼0.004 km s-1 km-1, which is characteristic for profile Quartz, forms a waveguide which gives rise to the teleseismic Pn. It is not necessary to include upper-mantle heterogeneity in order to explain the characteristics of this arrival.
KW - Crust
KW - Nuclear explosions
KW - Refraction seismology
KW - Scattering
KW - Seismic-wave propagation
KW - Upper-mantle
UR - http://www.scopus.com/inward/record.url?scp=0037325349&partnerID=8YFLogxK
U2 - 10.1046/j.1365-246X.2003.01873.x
DO - 10.1046/j.1365-246X.2003.01873.x
M3 - Article
AN - SCOPUS:0037325349
SN - 0956-540X
VL - 152
SP - F1-F7
JO - Geophysical Journal International
JF - Geophysical Journal International
IS - 2
ER -