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Denolle, Marine

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Denolle

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Marine

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Denolle, Marine
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    Retrieving Impulse Response Function Amplitudes From the Ambient Seismic Field
    (Oxford University Press (OUP), 2017) Viens, Loïc; Denolle, Marine; Miyake, Hiroe; Sakai, Shin’ichi; Nakagawa, Shigeki
    Seismic interferometry is now widely used to retrieve the impulse response function of the Earth between two distant seismometers. The phase information has been the focus of most passive imaging studies, as conventional seismic tomography uses traveltime measurements. The amplitude information, however, is harder to interpret because it strongly depends on the distribution of ambient seismic field sources and on the multitude of processing methods. Our study focuses on the latter by comparing the amplitudes of the impulse response functions calculated between seismic stations in the Kanto sedimentary basin, Japan, using several processing techniques. This region provides a unique natural laboratory to test the reliability of the amplitudes with complex wave propagation through the basin, and dense observations from the Metropolitan Seismic Observation network. We compute the impulse response functions using the cross correlation, coherency and deconvolution techniques of the raw ambient seismic field and the cross correlation of 1-bit normalized data. To validate the amplitudes of the impulse response functions, we use a shallow Mw 5.8 earthquake that occurred on the eastern edge of Kanto Basin and close to a station that is used as the virtual source. Both S and surface waves are retrieved in the causal part of the impulse response functions computed with all the different techniques. However, the amplitudes obtained from the deconvolution method agree better with those of the earthquake. Despite the expected wave attenuation due to the soft sediments of the Kanto Basin, seismic amplification caused by the basin geometry dominates the amplitudes of S and surface waves and is captured by the ambient seismic field. To test whether or not the anticausal part of the impulse response functions from deconvolution also contains reliable amplitude information, we use another virtual source located on the western edge of the basin. We show that the surface wave amplitudes of the anticausal part agree well with those of a shallow Mw 4.7 event that occurred close to the virtual source. This study demonstrates that the deconvolution technique seems to be the best strategy to retrieve reliable relative amplitudes from the ambient seismic field in the Kanto Basin.
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    Convolutional neural network for earthquake detection and location
    (American Association for the Advancement of Science (AAAS), 2018-02-02) Perol, Thibaut; Gharbi, Michaël; Denolle, Marine
    ConvNetQuake is the first neural network for detection and location of earthquakes from seismograms.
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    New perspectives on self-similarity for shallow thrust earthquakes
    (Wiley-Blackwell, 2016) Denolle, Marine; Shearer, Peter M.
    Scaling of dynamic rupture processes from small to large earthquakes is critical to seismic hazard assessment. Large subduction earthquakes are typically remote, and we mostly rely on teleseismic body waves to extract information on their slip rate functions. We estimate the P wave source spectra of 942 thrust earthquakes of magnitude Mw 5.5 and above by carefully removing wave propagation effects (geometrical spreading, attenuation, and free surface effects). The conventional spectral model of a single-corner frequency and high-frequency falloff rate does not explain our data, and we instead introduce a double-corner-frequency model, modified from the Haskell propagating source model, with an intermediate falloff of f−1. The first corner frequency f1 relates closely to the source duration T1, its scaling follows math formula for Mw<7.5, and changes to math formula for larger earthquakes. An elliptical rupture geometry better explains the observed scaling than circular crack models. The second time scale T2 varies more weakly with moment, math formula, varies weakly with depth, and can be interpreted either as expressions of starting and stopping phases, as a pulse-like rupture, or a dynamic weakening process. Estimated stress drops and scaled energy (ratio of radiated energy over seismic moment) are both invariant with seismic moment. However, the observed earthquakes are not self-similar because their source geometry and spectral shapes vary with earthquake size. We find and map global variations of these source parameters.
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    Multicomponent C3 Green’s Functions for Improved Long-Period Ground-Motion Prediction
    (Seismological Society of America (SSA), 2017-09-26) Sheng, Yixiao; Denolle, Marine; Beroza, Gregory
    The virtual earthquake approach to ground-motion prediction uses Green’s functions (GFs) determined from the ambient seismic field to predict long-period shaking from scenario earthquakes. The method requires accurate relative GF amplitudes between stations and among components; however, the amplitudes of ambient-field GFs are known to be subject to biases from uneven source distribution. We show that multicomponent, higher order cross correlations are significantly less biased than the conventional first-order cross correlation, and we demonstrate that they provide a more reliable prediction of observed ground-motion amplitudes for a recent moderate earthquake on the San Jacinto fault in southern California.