Deciphering shallow mantle stratification through information dimension

Abstract

Applying the concept of cluster entropy, we demonstrate that the primary P-to-s (Ps) conversions originating from the well-recognized seismological boundaries (Moho, 410 km, and 660 km depth interfaces) in Earth's interior and multiple refl ections (reverberations) between the surface and the Moho-the prominent crust-mantle boundary of Earth-can be unambiguously identifi ed. Their attendant information dimension can act as a discriminant. Documentation of shallow mantle stratifi cation at depths ~150-300 km (L/X layers) using Ps signals is scarce and is sometimes attributed to their weak registration in the seismograms together with interference by reverberations from shallow structure. The slopes of best fi ts to mean cluster information dimension (as function of epicentral distance) of Ps signals from target boundaries such as the Moho, 410 km, and L/X discontinuities are consistently gentle with a slight negative character. In contrast, those related to multiples show a steep positive behavior. This opposite nature can potentially discriminate between reverberations and direct converted waves, even when they tend to arrive in overlapping time windows. Our approach thus enables unequivocal identifi cation of shallow mantle layering from Ps data recorded at diverse tectonic provenances of wide antiquity.

Information theory–based measures of similarity for imaging shallow-mantle discontinuities

“…Our results show that information theory-based similarity measures can indeed distinctly and unambiguously discriminate between the primary converted phases and the reverberations. This study reinforces the presence of signifi cant velocity contrast features related to the Lehmann discontinuity depth beneath the Precambrian cratonic stations of India (Hyderabad and Cuddapah) and the Phanerozoic Pasadena station in the United States, as already reported by Ramesh et al (2010a). In addition, this method is tested to confi rm or negate the presence of midlithospheric discontinuities beneath stations Flin Flon and Harvard, North America.…”

“…The panacea proposed here is to transform our plane of observation from the measurement space to the generic space in order to discriminate the competing signals and characterize them based on several measures of similarities that stem from their associated entropy by applying the principles of Shannon's information theory. A beginning in this direction was initiated recently by us (see Ramesh et al, 2010a) based on the concepts of cluster entropy (Carbone et al, 2004;Balasis et al, 2009) and cross correlation (e.g., Arianos and Carbone, 2009). In this research article, we further expand our earlier studies and explore information-based similarities between the primary converted phases and the multiples employing a Gaussian distribution as a datum.…”

“…As a consequence, the presence of these three major boundaries (the Moho, 410 km, and 660 km) is robustly manifested in a wide variety of observations/data, both geophysical and geochemical, that represent and sample deep layers in Earth. However, issues related to the unambiguous detection of the possible presence of further stratifi cation, especially, at shallow-mantle depths (~150-300 km), particularly using Ps data, remain contentious (e.g., Sheehan et al, 2000;Li et al, 2002;Ramesh et al, 2010a). Essentially, complexities associated with registration and recognition of the direct converted signals originating from shallow-mantle target boundaries such as the Lehmann (Lehmann, 1959) and X-discontinuities (Revenaugh and Jordan, 1991) residing in the depth range of 150-300 km render them equivocal.…”

Imaging mantle lithosphere for diamond prospecting in southeast India

“…In earlier publications (see Ramesh et al, 2010aRamesh et al, , 2010bBapanayya et al, 2011), these positive-velocity-contrast seismic phases were interpreted as relict paleosubduction features based on their presentday depth disposition, and on fi eld geologic correlation and several other geophysical, geochemical, and age constraints. This interpretation is supported by: (1) the presence of nepheline syenites and carbonatites, which represent deformed alkaline rocks and carbonatites (DARCs), indicative of suturing in the study region (Leelanandam et al, 2006;Vijaya Kumar and Leelanandam, 2008); (2) 1.85 Ga sensitive high-resolution ion microprobe (SHRIMP) U-Pb ages of zircons separated from the Kandra ophiolite complex along the SE margin of India (Vijaya Kumar et al, 2010), suggestive of Wilson cycling; (3) documentation of a suite of rock occurrences in a particular sequence, along with their age constraints (Vijaya Kumar et al, 2011), reminiscent of the proposed subduction in southeast India; (4) a paired gravity anomaly in the region (Kaila and Bhatia, 1981), characteristic of suture zones; and (5) geophysically detected relict subduction features at depth from similar tectonic settings of Proterozoic age and younger Paleozoic times around the globe.…”

Sea surface temperatures in cooler climate stages bear more similarity with atmospheric CO2 forcing

“…Therefore, we explore the dynamic nonlinear interactions of several climate proxies applying information theory‐based stochastic methods that revolve around the concept of entropy or ensemble information content [ Shannon , 1948]. Very recently a small beginning is made in this emerging field of research related to climate modeling [ Larson , 2009; Majda and Gershgorin , 2011] and in solid earth geophysics too [e.g., Balasis et al , 2009; Ramesh et al , 2010; Bapanayya et al , 2011]. Perspectives to quantify data and model uncertainties associated with climate science by way of empirical relations are developed based on information theory to identify critical climate change directions of the present climate [ Majda and Gershgorin , 2011].…”