Global Distribution of Crustal Material Inferred by Seismology

Global Distribution of Crustal Material Inferred by Seismology Nozomu Takeuchi (ERI, Univ of Tokyo) (1) Importance of Directional Measurements from geophysicists’ point of view (2) Improvements of Neutrino Flux Modeling in the seismological aspects

Parameters Required for Geo-neutrino Simulation = Parameters Resolved by Geo-neutrino Observation • Earth’s Composition (compositions of crust & mantle) • Earth’s Structure (distributions of crustal materials) Approach for Retrieving Earth’s Structure • “Geophysical Decomposition” as a tool for interpretation of the observed data Importance of directional measurements

Fate of the Oceanic Crusts (1) Prediction by High Pressure Experiments Density measurements in the upper mantle conditions Ringwood & Irifune (1988) Oceanic crusts can be trapped around the 660, but finally entrained into the lower mantle.

Fate of the Oceanic Crusts (2) Suggestion by Mantle Convection Simulation Nakagawa & Tackley (2005) Oceanic crusts can sink into the lowermost mantle, and accumulate at the bottom of upwelling regions.

Fate of the Oceanic Crusts (3) Indirect Evidence by Seismic Tomography S velocity Bulk-sound velocity Masters et al. (2000) Chemical heterogeneities are suggested at the bottom of upwelling regions. possible accumulation of oceanic crusts

Example Classification of Geo-Neutrino Source (1) Surface Crust (2) Ambient Mantle (4) Crust at the bottom of upwelling regions (LLSVPs) detector ust (3) Crust in and around Subducting Slabs tal n e tin con cr oce an ic c rus t Can we decompose the observed flux into the above four components? We can utilize differences in incoming directions (directivities).

Expected Directivity by the Surface Crust (1) Formulation by Enomoto et al. (2007) V neutrino flux = at the detector (r’) decay rate x Intensity Factor from j-th Directional Bin intensity factor determined by source distributions

Expected Directivity by the Surface Crust (2) N W E S distance from the center bottoming radius direction from the center azimuth painted color

Difference in Expected Directivities N W 240 -290 km depth E S +2% +1% 550 -630 km depth Obayashi et al. (2009)

“Geophysical Decomposition” As an Interpretation Tool : incident angle : incident azimuth reference model : Coefficients can be determined by solving an inverse problem. larger mass fraction of depleted mantle? anomalies in bulk composition of the Earth? entrainments of continental crust? megalith on the 660? enriched elements in the lowermost mantle?

Appropriate Choice of the Tomography Models (short period data) (broadband data) Fukao et al. (2001)

Type of Seismic Data short period (high sensitivity) sensor broadband sensor

Usefulness of Broadband Waveforms all frequencies 0. 01 -0. 05 Hz 0. 1 -0. 5 Hz 0. 5 -1 Hz 1 -5 Hz 5 -10 Hz Short period data broadband data 0. 05 -0. 1 Hz

Comparison of Station Coverage Broadband data short period data 200 stations 20, 000 stations homogeneous heterogeneous

Data Type and Obtained Tomography Models broadband data 500 km depth Masters et al. (2000) Short period data 500 km depth Bijwaard et al. (1998) Models Obtained by Using broadband data : overall structures, structures beneath oceans short period data : detailed structures in subduction zones

Difficulties to Obtain Data-Based Crustal Models • Current global model (CRUST 2. 0) is not fully data-based. • Too thin to resolve the global map. • Sensitive frequency band is very “noisy”. Recent Progresses in Seismology • Dense broadband arrays with sufficient resolving power. • Use of “noise” to reveal crustal structures.

Improvements in Crust Models (1) Mapping by Broadband Data Dense broadband arrays are beginning to reveal crustal maps Zheng et al. (2011)

Improvements in Crust Models (2) Future Challenge Broadband networks installed by ERI • Use of broadband OBS data • Data based crustal map in wide areas around Japan

Challenge to Detection of Crusts in the Mantle (1) coherent phase incoherent phase (scattered waves) Station 1 Station 2 Conventional tomography Station 3 coherent phase: sensitive to larger-scale structures incoherent phase: sensitive to smaller-scale structures This Study

Challenge to Detection of Crusts in the Mantle (2) Required Resolution Current Resolution Use of incoherent phases may fill the gap between supply and demand.

Summary of The Talk • “Geophysical Decomposition” Importance of Directional Measurements • Data Based Seismological Earth Models Use of “noise” in our broadband OBS Use of “incoherence” in seismic waveforms