TY - JOUR
T1 - Seismological constraints on the ultralow velocity zones in the lowermost mantle from core-reflected waves
AU - Idehara, Koki
AU - Yamada, Akira
AU - Zhao, Dapeng
N1 - Funding Information:
We thank the data centers of the Hi-net and the International Monitoring System for providing us the waveform data. We are grateful to Taku Tsuchiya for discussion on mineral physics of the lowermost mantle, Ban-Yuan Kuo and Satoru Tanaka for valuable suggestions on array analyses and O.P. Mishra for comments on the manuscript, and George Helffrich, S. Rost and an anonymous reviewer for the helpful reviews of the manuscript. All the figures are made by using GMT (Wessel and Smith, 1995) . This work was partially supported by a research grant (Kiban-A 17204037) from Japan Society for the Promotion of Science to D. Zhao and A. Yamada.
PY - 2007/11/15
Y1 - 2007/11/15
N2 - Analyses of reflected seismic phases PcP and ScP from the core-mantle boundary (CMB) enable us to constrain the physical properties of the ultralow velocity zones (ULVZs) at the base of the mantle. The CMB region beneath the western and southern Pacific is investigated in detail by using a large amount of waveform data recorded by the short-period array stations. Clear arrivals of postcursor to ScP (ScsP) are detected from several event-receiver pairs, which sample the CMB regions beneath Philippine-Kalimantan and East of Australia, indicating the existence of ULVZs under the regions. No ScP precursors (SdP and SPcP) are found in our data set except for a few events with a large epicentral distance over 45°. No additional arrivals related to PcP are found in the region where ScsP is observed in the ScP wavelet. Elastic properties of the ULVZ are precisely constrained by waveform modeling of both PcP and ScP which sample the CMB region under Philippine-Kalimantan. Different ULVZ structures are found between the northeastern and southwestern parts of the Philippine-Kalimantan: the ratio of shear-to-compressional velocity reductions is 2.0-2.5 and the ratio of density-to-shear velocity changes is - 0.5 to - 0.33 in the northeastern part, while minimal changes in compressional velocity and large shear velocity decrease in the southwestern part are found. A certain degree of density increases and shear velocity decreases are also observed in the ULVZ beneath East of Australia. Increase in density and decrease in shear velocity throughout our observation imply that the iron incorporation into the lowermost mantle minerals may generate the ULVZ anomaly. However, other mechanisms such as partial melting can explain the structural difference between the northeastern and southwestern parts of the ULVZ beneath the Philippine-Kalimantan region.
AB - Analyses of reflected seismic phases PcP and ScP from the core-mantle boundary (CMB) enable us to constrain the physical properties of the ultralow velocity zones (ULVZs) at the base of the mantle. The CMB region beneath the western and southern Pacific is investigated in detail by using a large amount of waveform data recorded by the short-period array stations. Clear arrivals of postcursor to ScP (ScsP) are detected from several event-receiver pairs, which sample the CMB regions beneath Philippine-Kalimantan and East of Australia, indicating the existence of ULVZs under the regions. No ScP precursors (SdP and SPcP) are found in our data set except for a few events with a large epicentral distance over 45°. No additional arrivals related to PcP are found in the region where ScsP is observed in the ScP wavelet. Elastic properties of the ULVZ are precisely constrained by waveform modeling of both PcP and ScP which sample the CMB region under Philippine-Kalimantan. Different ULVZ structures are found between the northeastern and southwestern parts of the Philippine-Kalimantan: the ratio of shear-to-compressional velocity reductions is 2.0-2.5 and the ratio of density-to-shear velocity changes is - 0.5 to - 0.33 in the northeastern part, while minimal changes in compressional velocity and large shear velocity decrease in the southwestern part are found. A certain degree of density increases and shear velocity decreases are also observed in the ULVZ beneath East of Australia. Increase in density and decrease in shear velocity throughout our observation imply that the iron incorporation into the lowermost mantle minerals may generate the ULVZ anomaly. However, other mechanisms such as partial melting can explain the structural difference between the northeastern and southwestern parts of the ULVZ beneath the Philippine-Kalimantan region.
KW - Core-reflected waves
KW - Iron intrusion
KW - Partial melting
KW - Ultralow velocity zone (ULVZ)
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U2 - 10.1016/j.pepi.2007.07.005
DO - 10.1016/j.pepi.2007.07.005
M3 - Article
AN - SCOPUS:35548942154
VL - 165
SP - 25
EP - 46
JO - Physics of the Earth and Planetary Interiors
JF - Physics of the Earth and Planetary Interiors
SN - 0031-9201
IS - 1-2
ER -