Collaborative Research: Incorporating SPECFEM3D Numerical Seismograms in the Global CMT Project

Lead PI: Goran Ekstrom , Meredith Nettles

Unit Affiliation: Seismology, Geology and Tectonophysics, Lamont-Doherty Earth Observatory (LDEO)

September 2022 - August 2024
Active
North America ; United States
Project Type: Research

DESCRIPTION: This research will lay the groundwork for improvements in the scientific description of earthquakes, benefitting researchers in earthquake statistics, seismic tomography, seismic hazard, and seismic discrimination, as well as tectonic interpretation and analysis. This is the first step towards making the results of complex and expensive numerical calculations available for multiple applications and a wide range of users. This work focuses on demonstrating the feasibility of the methodology, but the database and method will be valuable for any research requiring accurate predictions of the global seismic wavefield from an arbitrary earthquake at any location without expensive computation. Two graduate students will be trained in research at the nexus of earthquake science, theoretical seismology, and computational Earth science.

This two-year, focused effort will (1) develop a new method for calculating, storing, and accessing high-fidelity long-period synthetic seismograms for state-of-the-art 3D tomographic models of the Earth, and (2) incorporate these seismograms in the earthquake analysis of the Global Centroid-Moment-Tensor (CMT) Project. Currently, the CMT synthetic seismograms are calculated using modern 3D Earth models, but accuracy is limited by the validity of the path-average approximation for mode summation and surface-wave ray theory, inexact predictions of the amplitude and polarization of ground motion, and other unmodeled effects, bias retrieved earthquake parameters. The incorporation of higher-fidelity synthetic seismograms in the CMT analysis will improve the characterization of seismic sources and remove concerns about a key source of uncertainty and bias. The team will adapt the spectral-element wave-equation solver SPECFEM3D_GLOBE to generate a database of kernel seismograms on a global grid of hypocenters, for a large set of station locations, using source-receiver reciprocity to speed up the calculation. Kernel seismograms on the grid will be organized and stored in a format that facilitates rapid access to a particular source region and the stations of the Global Seismographic Network. Kernel seismograms for an arbitrary centroid location will be efficiently calculated by spatial interpolation, in a manner that matches the accuracy of the full forward calculation. The CMT code will be modified to ingest the interpolated SPECFEM3D_GLOBE seismograms and testing will allow the assessment of success of the approach and method. The Princeton numerical seismology group and Lamont earthquake-analysis group will jointly evaluate the approach and fidelity of the waveform interpolation, develop practical formats for accessing the (massive) database of global waveforms, and assess the success of these developments.

BROADER IMPACTS: The proposed developments will lay the groundwork for improvements in the systematic generation of CMT solutions, benefitting researchers in earthquake statistics, seismic tomography, seismic hazard, and seismic discrimination, as well as tectonic interpretation and analysis. The development of a database of pre-calculated accurate kernel seismograms for arbitrary source locations and globally distributed stations is the first step towards making the results of complex and expensive numerical calculations available for multiple applications and a wide range of users. Our proposed work focuses on demonstrating the feasibility of the Global CMT use case, but the database and method will be valuable for any research requiring accurate predictions of the global wavefield from an arbitrary source at any location without expensive computation. Two graduate students will be trained in research at the nexus of earthquake science, theoretical seismology, and computational Earth science.

SPONSOR:

National Science Foundation

FUNDED AMOUNT:

$251,993

RESEARCH TEAM:

Jeroen Tromp

EXTERNAL COLLABORATORS:

Princeton University

WEBSITE:

https://www.nsf.gov/awardsearch/showAward?AWD_ID=2218793