Emmanuel Soliman Mortel Garcia
@kyoto-u.ac.jp
Program-Specific Researcher, Earthquake Hazards Research Center, Disaster Prevention Research Institute
Kyoto University
Scopus Publications
Scholar Citations
Scholar h-index
Scholar i10-index
Scopus Publications
Atikul Haque Farazi, Yoshihiro Ito, Emmanuel Soliman M Garcia, Agostiny Marrios Lontsi, Francisco José Sánchez-Sesma, Aristoteles Jaramillo, Shukei Ohyanagi, Ryota Hino, and Masanao Shinohara
Oxford University Press (OUP)
SUMMARYThis study presents the shear wave velocity (VS) structures of sedimentary sequences and a section of the upper crustal layer in the Fukushima forearc region of the Japan Trench subduction zone, which were obtained by analysing the horizontal-to-vertical (H/V) spectral ratios of ambient vibration records. The H/V curves were derived using 31 d of continuous seismic data from 3 broad-band and 16 short-period ocean bottom seismometer (OBS) stations. Using the broad-band data, H/V ratios from 0.01 to 10 Hz were derived, but the ratios below 0.1 Hz frequencies were unusually large and temporally unstable. Characterization of seismic noise energy from ∼1 yr of seismic data of three broad-band OBSs revealed variable and elevated energy conditions below 0.1 Hz due to typical long-period oceanic noise; we link these observations with the unstable H/V ratios below this frequency. Therefore, H/V analysis was performed in the frequency range of 0.1–10 Hz for both broad-band and short-period OBSs to obtain subsurface VS profiles. For the forward calculation of the H/V ratios in the inversion process, we used the recently developed ‘hvgeneralized’ method, which is based on the diffuse field assumption, and accounts for the water layer on top of stratified media. Moreover, available prior geological and geophysical information was utilized during the inversion of the H/V curves. We found that subsurface VS ranged from approximately 30 m s−1 at the seabed to approximately 4900 m s−1 at 7000 m below the sea floor (mbsf). Starting with the best model candidate at each OBS location, the effect of the water layer on the H/V curve in the deep ocean was investigated by comparing synthetic H/V curves with and without the water layer. The synthetic H/V analysis revealed that the water layer had a significant effect on H/V amplitudes at higher frequencies (>1 Hz), whereas comparatively little effect was observed at lower frequencies (<1 Hz). This study provides an empirical basis for H/V analysis using OBS data to determine VS down to several kilometres of sedimentary sequences to the upper crust with high-resolution.
Yasunori Sawaki, Yusuke Yamashita, Shukei Ohyanagi, Emmanuel Soliman M Garcia, Aki Ito, Hiroko Sugioka, Tsutomu Takahashi, Masanao Shinohara, and Yoshihiro Ito
Oxford University Press (OUP)
SUMMARY This study evaluates the seafloor ambient noise environment that varies with the water depth based on a correction analysis of the horizontal sensor orientation for ocean-bottom seismographs. As ocean-bottom seismographs are mainly deployed as ‘free-fall’ installations, we have no information on which direction a horizontal sensor faces at the seafloor. An accurate sensor orientation is crucial for data processing based on seismic wavefields. Among several seismological approaches that use passive sources to correct the horizontal sensor azimuth, the particle motion of teleseismic Rayleigh waves is widely used for broad-band ocean-bottom seismographs. We performed seafloor seismic observations in the Hyuga-nada region at the western end of the Nankai subduction zone and deployed broad-band and short-period seismographs. However, studies have yet to investigate whether orientation correction via the Rayleigh-wave polarization method is valid for short-period data. The results of the Rayleigh wave method from our campaign observation data showed that the estimation uncertainty of short-period sensor orientations increased with a decreasing water depth; we observed a transition depth for the uncertainty at 2200–2600 m. The measurement quality, or the cross-correlation coefficient between the radial and Hilbert-transformed vertical components, also decreased at depths shallower than 2000 m. Moreover, an analysis of the noise power spectral densities showed that ambient noise levels during long periods (>10 s) increased with decreasing depth. Infragravity waves controlled vertical long-period noise levels, while ocean currents dominated horizontal long-period noise; both of these reduced the Rayleigh-wave signals as a function of environmental noise. Infragravity waves also likely distorted the Rayleigh waveforms. Both mechanisms contributed to the sudden rise in orientation uncertainty and low measurement quality at shallow stations (i.e. <2000 m). We confirmed that the variation in orientation uncertainty with the water depth can be used as an index for the ambient noise environment of the seafloor.
R. Plata-Martinez, S. Ide, M. Shinohara, E. S. Garcia, N. Mizuno, L. A. Dominguez, T. Taira, Y. Yamashita, A. Toh, T. Yamada,et al.
Springer Science and Business Media LLC
AbstractThe Guerrero seismic gap is presumed to be a major source of seismic and tsunami hazard along the Mexican subduction zone. Until recently, there were limited observations at the shallow portion of the plate interface offshore Guerrero, so we deployed instruments there to better characterize the extent of the seismogenic zone. Here we report the discovery of episodic shallow tremors and potential slow slip events in Guerrero offshore. Their distribution, together with that of repeating earthquakes, seismicity, residual gravity and bathymetry, suggest that a portion of the shallow plate interface in the gap undergoes stable slip. This mechanical condition may not only explain the long return period of large earthquakes inside the gap, but also reveals why the rupture from past M < 8 earthquakes on adjacent megathrust segments did not propagate into the gap to result in much larger events. However, dynamic rupture effects could drive one of these nearby earthquakes to break through the entire Guerrero seismic gap.
Tomohiro Inoue, Yoshihiro Ito, Laura M. Wallace, Yutaka Yoshikawa, Daisuke Inazu, Emmanuel Soliman M. Garcia, Tomoya Muramoto, Spahr C. Webb, Kazuaki Ohta, Syuichi Suzuki,et al.
American Geophysical Union (AGU)
Isolating the source of nontidal oceanographic noise in seafloor pressure data is critical for improving the use of these data for seafloor geodetic applications. Residuals between nearby bottom pressure records have typically been used to remove the nontidal components, as these are largely common‐mode. To evaluate the similarities between pairs of observed bottom pressure records at a range of water depths, we calculate the standard deviations of the time series of residuals between data from all site pairs, installed in the Hikurangi subduction zone offshore New Zealand. We find that the magnitude of the standard deviation depends more on relative water depth than the distance between sites. This confirms the result of previous studies from Cascadia that nontidal components are more similar along isobaths even if the distance between sites is large. Furthermore, in order to reduce noises, the required depth difference between site pairs also varies with site depths.
Jan Černý, María Teresa Ramírez-Herrera, Emmanuel Soliman Garcia, and Yoshihiro Ito
Elsevier BV
Emmanuel Soliman M Garcia, David T Sandwell, and Dan Bassett
Oxford University Press (OUP)
SUMMARY Flexure and fracturing of the seafloor on the outer trench wall of subduction zones reflect bending of the lithosphere beyond its elastic limit. To investigate these inelastic processes, we have developed a full nonlinear inversion approach for estimating the bending moment, curvature and outer trench wall fracturing using shipboard bathymetry and satellite altimetry-derived gravity data as constraints. Bending moments and downward forces are imposed along curved trench axes and an iterative method is used to calculate the nonlinear response for 26 sites in the circum-Pacific region having seafloor age ranging from 15 to 148 Ma. We use standard thermal and yield strength envelope models to develop the nonlinear moment versus curvature relationship. Two coefficients of friction of 0.6 and 0.3 are considered and we find that the lower value provides a better overall fit to the data. The main result is that the lithosphere is nearly moment saturated at the trench axis. The effective elastic thickness of the plate on the outer trench slope is at least three times smaller than the elastic thickness of the plate before bending at the outer rise in agreement with previous studies. The average seafloor depth of the unbent plate in these 26 sites matches the Parsons & Sclater depth versus age model beyond 120 Ma. We also use the model to predict the offsets of normal faults on the outer trench walls and compare this with the horst and graben structures observed by multibeam surveys. The model with the lower coefficient of friction fits the fault offset data close to the trench axis. However, the model predicts significant fracturing of the lithosphere between 75 and 150 km away from the trench axis where no fracturing is observed. To reconcile these observations, we impose a thermoelastic pre-stress in the lithosphere prior to subduction. This pre-stress delays the onset of fracturing in better agreement with the data.
Diego Melgar, Angel Ruiz-Angulo, Emmanuel Soliman Garcia, Marina Manea, Vlad. C. Manea, Xiaohua Xu, M. Teresa Ramirez-Herrera, Jorge Zavala-Hidalgo, Jianghui Geng, Nestor Corona,et al.
Springer Science and Business Media LLC
Víctor M. Cruz‐Atienza, Yoshihiro Ito, Vladimir Kostoglodov, Vala Hjörleifsdóttir, Arturo Iglesias, Josué Tago, Marco Calò, Jorge Real, Allen Husker, Satoshi Ide,et al.
Seismological Society of America (SSA)
The historical record of large subduction earthquakes in Guerrero, Mexico, reveals the existence of an ∼230 km length segment below the coast where no major rupture has occurred in the past 60 years. Reliable quantification of the hazard associated with such a seismic gap is urgently needed for risk mitigation purposes by means of state-of-the-art observations and modeling. In this article, we introduce and quantitatively assess the first seismogeodetic amphibious network deployed in Mexican and Central American soils that will provide the opportunity to achieve this goal in the near future. Deployed in 2017, the network is the result of a collaborative effort between Mexican and Japanese scientists. It consists of 15 onshore broadband and 7 ocean-bottom seismometers, 33 Global Positioning System (GPS) stations, 7 ocean-bottom pressure gauges, and 2 GPSacoustic sites, most of them installed within the Guerrero seismic gap. Initial data from the network revealed the occurrence of a 6-month-long slow-slip event in Guerrero, starting in May and ending in October 2017. To illustrate the performance of the various instruments, we also present the first ocean-bottom pressure and GPS-acoustic measurements in Mexico; the latter was obtained by means of an autonomousWave Glider vehicle. The ground motion of the devastating 19 September 2017 Mw 7.1 earthquake in central Mexico is presented as well. Nominal resolution of the seismogeodetic network is estimated through different synthetic inversion tests for tomographic imaging and the seismic coupling (or slow-slip) determination on the plate interface. The tests show that combined onshore and offshore instruments should lead to unprecedented results regarding the seismic potential (i.e., interface coupling) of the seismic gap and the Earth structure from the Middle America trench up to 70-km depth across the Guerrero state.
Emmanuel S. Garcia, David T. Sandwell, and Karen M. Luttrell
Oxford University Press (OUP)
S U M M A R Y Thin plate flexure theory provides an accurate model for the response of the lithosphere to vertical loads on horizontal length scales ranging from tens to hundreds of kilometres. Examples include flexure at seamounts, fracture zones, sedimentary basins and subduction zones. When applying this theory to real world situations, most studies assume a locally uniform plate thickness to enable simple Fourier transform solutions. However, in cases where the amplitude of the flexure is prominent, such as subduction zones, or there are rapid variations in seafloor age, such as fracture zones, these models are inadequate. Here we present a computationally efficient algorithm for solving the thin plate flexure equation for non-uniform plate thickness and arbitrary vertical load. The iterative scheme takes advantage of the 2-D fast Fourier transform to perform calculations in both the spatial and spectral domains, resulting in an accurate and computationally efficient solution. We illustrate the accuracy of the method through comparisons with known analytic solutions. Finally, we present results from three simple models demonstrating the differences in trench outer rise flexure when 2-D variations in plate rigidity and applied bending moment are taken into account. Although we focus our analysis on ocean trench flexure, the method is applicable to other 2-D flexure problems having spatial rigidity variations such as seamount loading of a thermally eroded lithosphere or flexure across the continental–oceanic crust boundary.
David T. Sandwell, R. Dietmar Müller, Walter H. F. Smith, Emmanuel Garcia, and Richard Francis
American Association for the Advancement of Science (AAAS)
High-resolution tectonic solutions Detailed topographic maps are available for only a small fraction of the ocean floor, severely limited by the number of ship crossings. Global maps constructed using satellite-derived gravity data, in contrast, are limited in the size of features they can resolve. Sandwell et al. present a new marine gravity model that greatly improves this resolution (see the Perspective by Hwang and Chang). They identify several previously unknown tectonic features, including extinct spreading ridges in the Gulf of Mexico and numerous uncharted seamounts. Science , this issue p. 65 ; see also p. 32
Emmanuel S. Garcia, David T. Sandwell, and Walter H.F. Smith
Oxford University Press (OUP)
1 . The arrival time estimated from the fit of the analytical model to the nadir-pointing SAMOSA data agreed to better than 1 mm in absolute range. The σ parameter from the least-squares model fit shows a good linear relationship with the SWH for the SAMOSA data with a misfit at smaller SWH due to the detailed shape of the point target response function not being fully characterized by our Gaussian analytic formulation. This comparison confirms that our model is a good description of the single-look, nadir-pointing case.
David Sandwell, Emmanuel Garcia, Khalid Soofi, Paul Wessel, Michael Chandler, and Walter H. F. Smith
Society of Exploration Geophysicists
More than 60% of the Earth's land and shallow marine areas are covered by > 2 km of sediments and sedimentary rocks, with the thickest accumulations on rifted continental margins (Figure 1). Free-air marine gravity anomalies derived from Geosat and ERS-1 satellite altimetry (Fairhead et al., 2001; Sandwell and Smith, 2009; Andersen et al., 2009) outline most of these major basins with remarkable precision. Moreover, gravity and bathymetry data derived from altimetry are used to identify current and paleo-submarine canyons, faults, and local recent uplifts. These geomorphic features provide clues to where to look for large deposits of sediments. While current altimeter data delineate large offshore basins and major structures, they do not resolve some of the smaller geomorphic features and basins (Yale et al., 1998; Fairhead et al., 2001). Improved accuracy and resolution is desirable: to facilitate comparisons between continental margins; as an exploration tool and to permit extrapolation of known structures from well-surveyed areas; to follow fracture zones out of the deep-ocean basin into antecedent continental structures, to define and compare segmentation of margins along strike and identify the position of the continent-ocean boundary; and to study mass anomalies (e.g., sediment type and distribution) and isostatic compensation at continental margins. In this article, we assess the accuracy of a new global marine gravity model based on a wealth of new radar altimetry data and demonstrate that these gravity data are superior in quality to the majority of publicly available academic and government ship gravity data.