TY - JOUR
T1 - Dynamical links between small- and large-scale mantle heterogeneity
T2 - Seismological evidence
AU - Frost, Daniel A.
AU - Garnero, Edward
AU - Rost, Sebastian
N1 - Funding Information:
This work was supported NSF grant EAR1401270 and NERC grants NE/K006290/1 and NE/H022473/1 . CTBT International Monitoring System data used here were acquired while the author was undertaking a studentship sponsored by the UK National Data Centre at AWE Blacknest. The paper benefited from discussions with Barbara Romanowicz, and improved from helpful comments of two reviewers.
Publisher Copyright:
© 2017 Elsevier B.V.
PY - 2018/1/15
Y1 - 2018/1/15
N2 - We identify PKP•PKP scattered waves (also known as P′•P′) from earthquakes recorded at small-aperture seismic arrays at distances less than 65°. P′•P′ energy travels as a PKP wave through the core, up into the mantle, then scatters back down through the core to the receiver as a second PKP. P′•P′ waves are unique in that they allow scattering heterogeneities throughout the mantle to be imaged. We use array-processing methods to amplify low amplitude, coherent scattered energy signals and resolve their incoming direction. We deterministically map scattering heterogeneity locations from the core–mantle boundary to the surface. We use an extensive dataset with sensitivity to a large volume of the mantle and a location method allowing us to resolve and map more heterogeneities than have previously been possible, representing a significant increase in our understanding of small-scale structure within the mantle. Our results demonstrate that the distribution of scattering heterogeneities varies both radially and laterally. Scattering is most abundant in the uppermost and lowermost mantle, and a minimum in the mid-mantle, resembling the radial distribution of tomographically derived whole-mantle velocity heterogeneity. We investigate the spatial correlation of scattering heterogeneities with large-scale tomographic velocities, lateral velocity gradients, the locations of deep-seated hotspots and subducted slabs. In the lowermost 1500 km of the mantle, small-scale heterogeneities correlate with regions of low seismic velocity, high lateral seismic gradient, and proximity to hotspots. In the upper 1000 km of the mantle there is no significant correlation between scattering heterogeneity location and subducted slabs. Between 600 and 900 km depth, scattering heterogeneities are more common in the regions most remote from slabs, and close to hotspots. Scattering heterogeneities show an affinity for regions close to slabs within the upper 200 km of the mantle. The similarity between the distribution of large-scale and small-scale mantle structures suggests a dynamic connection across scales, whereby mantle heterogeneities of all sizes may be directed in similar ways by large-scale convective currents.
AB - We identify PKP•PKP scattered waves (also known as P′•P′) from earthquakes recorded at small-aperture seismic arrays at distances less than 65°. P′•P′ energy travels as a PKP wave through the core, up into the mantle, then scatters back down through the core to the receiver as a second PKP. P′•P′ waves are unique in that they allow scattering heterogeneities throughout the mantle to be imaged. We use array-processing methods to amplify low amplitude, coherent scattered energy signals and resolve their incoming direction. We deterministically map scattering heterogeneity locations from the core–mantle boundary to the surface. We use an extensive dataset with sensitivity to a large volume of the mantle and a location method allowing us to resolve and map more heterogeneities than have previously been possible, representing a significant increase in our understanding of small-scale structure within the mantle. Our results demonstrate that the distribution of scattering heterogeneities varies both radially and laterally. Scattering is most abundant in the uppermost and lowermost mantle, and a minimum in the mid-mantle, resembling the radial distribution of tomographically derived whole-mantle velocity heterogeneity. We investigate the spatial correlation of scattering heterogeneities with large-scale tomographic velocities, lateral velocity gradients, the locations of deep-seated hotspots and subducted slabs. In the lowermost 1500 km of the mantle, small-scale heterogeneities correlate with regions of low seismic velocity, high lateral seismic gradient, and proximity to hotspots. In the upper 1000 km of the mantle there is no significant correlation between scattering heterogeneity location and subducted slabs. Between 600 and 900 km depth, scattering heterogeneities are more common in the regions most remote from slabs, and close to hotspots. Scattering heterogeneities show an affinity for regions close to slabs within the upper 200 km of the mantle. The similarity between the distribution of large-scale and small-scale mantle structures suggests a dynamic connection across scales, whereby mantle heterogeneities of all sizes may be directed in similar ways by large-scale convective currents.
KW - deep Earth
KW - mantle dynamics
KW - mantle structure
KW - scattering
KW - seismic arrays
KW - seismology
UR - http://www.scopus.com/inward/record.url?scp=85033702404&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85033702404&partnerID=8YFLogxK
U2 - 10.1016/j.epsl.2017.10.058
DO - 10.1016/j.epsl.2017.10.058
M3 - Article
AN - SCOPUS:85033702404
SN - 0012-821X
VL - 482
SP - 135
EP - 146
JO - Earth and Planetary Sciences Letters
JF - Earth and Planetary Sciences Letters
ER -