Li Zhao - US grants

Zhao, Li

The focus of this proposal is to develop a high-resolution tomography method for seismic arrays. Resolution to sub-array structure is enhanced by inverting the phase and amplitude variations between adjacent stations, rather than at individual stations, in order to minimize biases caused by uncertainties in lateral heterogeneities far away from the array. Frechet kernels of the data are calculated by coupled normal-mode summation so that all finite-frequency effects are accounted for with no high-frequency or averaging approximations. A new traveling-wave method will also be developed to calculate exact kernels near stations. Asymptotic Legendre functions are used to express waves from the source to sub-array heterogeneity (scatterer), but exact Legendre functions are adopted for waves from the scatterer to the station.


The tomography method is being developed for the Southern Africa Seismic Array, deployed to study the Kaapvaal craton, and 3-D inversions are conducted for upper-mantle anisotropic structure. Data are measured for surface and upper-mantle body waves at an average of 50 three-component stations from 51 teleseismic events. The result will shed new light on the conflicting features in some of the recent regional models, such as the presence of an oceanic-type low-velocity zone beneath the craton and shear-wave anisotropy. The multi-station, full-wave method developed here is also well suited to serve the need of the upcoming USArray. With its proposed average spacing of about 70 km between adjacent stations, this method will be able to provide a nearly uniform lateral resolution of about 50 km in the upper mantle over the entire continental United States.

Zhao
EAR-0308403

In this proposal, the PI plans to conduct a regional three-dimensional (3-D) tomography for the anisotropic shear-wave velocity in the mantle beneath Eastern Asia. This study will be carried out by taking advantage of a wide distribution of moderate-sized (magnitude 5-6) earthquakes in most parts of Eastern Asia, an increasing number of permanent seismic stations and the latest developments in the methodology for regional tomography. The data to be inverted will include the frequency-dependent travel-time and amplitude perturbations measured on intermediate-period (20-100s) three-component seismic records of surface waves, mantle-turning body waves and ScS reverberations. Moreover, these measurements obtained from regional, intermediate-period seismic waves will be inverted using accurate and realistic full 3-D Frechet kernels computed by a normal-mode coupling algorithm. The model parameters will include the 3-D radially-anisotropic shear-wave velocity and the topographies of the upper-mantle transition-zone discontinuities. In most parts of the region under study, the upper-mantle structure will be resolved on a horizontal scale of ~500 km and a vertical scale of ~100 km. Issues affecting tomography models, such as source-receiver coverage, inversion procedures, velocity-topography trade-off, anisotropy, and attenuation will be examined. This is the first application of full 3-D regional tomography approach to a continental region. It is also the first study in which the perturbations in velocity and discontinuity topography are jointly inverted. The results will provide constraints for the geodynamic evolution of Eastern Asia and its relation to surrounding tectonic regions. Broader impact: The PI works closely with graduate students on this and related regional tomography studies and methods and data and software will also be made available to the wider seismology community. The techniques developed here can be an ideal choice for other regional tomography studies, for example the mantle structure under the USArray.
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PROJECT SUMMARY The goal of this research proposal is to dissect the novel regulatory circuits and genes underlying novel traits, to get a better understanding of the genetic basis of morphological and cellular innovation. Every morphological structure or trait originated at some time point in the past and evolved under various evolutionary paths. However, it is unknown how a novel trait originates and how gene and regulatory networks spatially orchestrate the development of the novel cell types, tissues, and organs. Identifying the processes driving and governing morphological and functional diversity and complexity is a major step towards understanding the evolution of complex life. However, our understanding of this process is still limited. The long-term goal of this research program is to functionally characterize the molecular genetic basis of novel cell clusters and novel morphological phenotypes. The central hypothesis is that evolutionary innovations emerging from novel regulatory networks depend on changes in transcription factors and enhancers. Guided by preliminary data including single cell RNA sequencing and well-established theories, the proposed research will test the central hypothesis using an integrative approach. We will determine: 1) regulatory network innovation in novel cell clusters in Drosophila, 2) enhancers responsible for transcription factor expression changes and downstream expression network modification, and 3) the genetic regulatory basis of a novel trait. We performed single-cell sequencing and RNA fluorescent in situ hybridization (FISH) on testis and found a novel cell cluster differentiated between Drosophila species. Combined with ATAC-sequencing data, we will use modeling and functional studies to study the genetic basis of the novel cell cluster. Following this hypothesis that novel enhancers of transcription factors (TFs) are essential for novel traits, we will study the cause of a recurrent novel trait and test the hypothesis that a novel regulatory circuit is essential for a novel trait. We hypothesize that novel enhancers or cis-regulatory motifs of TFs are essential for whole-genome level changes in chromatin accessibility. To test it, we will identify enhancer and motif changes between closely related species to provide insights into enhancer and TF binding affinity co- evolution. This study will provide important insights into the evolution of transcription regulatory networks and their contributions to novel morphological and cellular traits. Altogether, our integrative approach will help to elucidate the origination and evolution of novel regulatory circuits and their contributions to phenotypic innovation.