Fenglin niu
Rice University, Earth Science, Faculty Member
ABSTRACT El norte de Venezuela está ubicada en la zona de interacción de las placas del Caribe y de Sudamérica, lo que ha generado una compleja zona de interacción a nivel de las litosferas. Durante los estudios realizados en el marco de... more
ABSTRACT El norte de Venezuela está ubicada en la zona de interacción de las placas del Caribe y de Sudamérica, lo que ha generado una compleja zona de interacción a nivel de las litosferas. Durante los estudios realizados en el marco de los proyecto GEODINOS y BOLÍVAR desde el año 2003 se determinaron las principales estructuras del norte de Venezuela, tanto a nivel del manto como en la corteza. Los estudios sismológicos y gravimétricos se complementaron con estudios geológicos destinados a conocer la historia de deformación de las unidades metamórficas, así como las cuencas cuaternarias asociadas a los principales sistemas de deformación.
Research Interests: Geography and Humanities
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The perfectly matched layer (PML) boundary condition has been widely used as a very effective absorbing boundary condition for seismic wavefield simulations. Convolutional PML (CPML) achieved by using a complex frequency-shifted stretch... more
The perfectly matched layer (PML) boundary condition has been widely used as a very effective absorbing boundary condition for seismic wavefield simulations. Convolutional PML (CPML) achieved by using a complex frequency-shifted stretch function was the latest development to further improve PML’s absorption performance for near-grazing angle incident waves as well as for low-frequency incident waves. However, the mathematical theory of the PML method is derived from the first-order equation, all PML implementations of second-order equations are to introduce auxiliary equations or variables to rewrite original PML equations, which will complicate the implementation. In this article, we propose a simple and efficient CPML implementation method for the second-order elastic wave equation, which directly simulates the second-order CPML equation. The main advantage of this method is that there is no need to introduce auxiliary variables or auxiliary equations to convert the second-order PML equation from the complex coordinate space to the real axis. Comparedwith the conventional CPMLmethod for the secondorder elastic wave equation, it introduces only eight convolution variables. We demonstrate the validity and absorption performance through extensive numerical experiments. ARTICLE HISTORY Received 20 April 2021 Accepted 4 October 2021
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Research Interests: Geology and Seismology
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The geology of China has been found to be highly diverse, consisting of various tectonic zones from the ancient Archean Sino-Korean and Yangtze cratons to the young and active Tibetan Plateau formed by the Cenozoic India-Eurasia... more
The geology of China has been found to be highly diverse, consisting of various tectonic zones from the ancient Archean Sino-Korean and Yangtze cratons to the young and active Tibetan Plateau formed by the Cenozoic India-Eurasia collision. China is also a country with high levels of seismic activity, and has a history of strong earthquakes that caused great loss in both life and property. Therefore, knowledge of the anisotropic structure of the crust beneath China has great importance in understanding crustal and lithospheric deformation, as well as locating earthquake hypocenters and investigating the mechanism of strong earthquakes in China. We analyzed a large amount of high-quality broadband teleseismic receiver function data recorded by a total of 36 Chinese National Digital Seismic Network stations between September of 2000 and December of 2010. At each station, we collected more than 500 receiver functions, which showed a very good coverage in back azimuth that is required to...
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ABSTRACT The understanding of the depth dependency of the inner core attenuation is important to constrain the physical mechanism and state of the inner core but it is still controversial. In Iritani et al. [2010, GRL], we employed a... more
ABSTRACT The understanding of the depth dependency of the inner core attenuation is important to constrain the physical mechanism and state of the inner core but it is still controversial. In Iritani et al. [2010, GRL], we employed a waveform inversion method based on simulated annealing (SA) that enables to analyze complicated waveforms contaminated by phase overlaps, and applied it to Japanese Hi-net data. The attenuation model we obtained beneath the northeastern Pacific shows a gradual increase of the attenuation from ICB to 200 - 250 km depth and a decrease from this depth range and its possible relation to the growing process of the inner core was suggested (cf. Monnereau et al., 2010, Science). The purpose of this study is to investigate whether the attenuation structure obtained by analyzing Japanese data is just a local feature or more a general feature in the western hemisphere of the inner core. We apply the same method as Iritani et al. [2010] to the NECESSArray data. NECESSArray is a large temporary broadband seismic array installed in Northeastern China (from Sep. 2009 to August 2011). Core phases observed by this array for earthquakes occurred in South America region pass in the inner core beneath central Canada and together with the Japanese data coverage, a wide region of the western hemisphere can be sampled. We have so far analyzed triplicated core phase data for 6 events occurred in South America. Measured attenuation parameters show a gradual increase with distance and that is consistent with the result of Iritani et al. [2010]. It suggests that a similar structure extends widely beneath the North American continent and that the obtained attenuation structure may be representative structure of the western hemisphere.
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Research Interests: Geology, China, Seismology, Tomography, Upwelling, and 3 moreSeismic Tomography, Mantle plume, and Plume
ABSTRACT We have used 4th root receiver function stacks, and pre-stack receiver function depth migrations to study the transition zone discontinuity structure beneath southwestern Japan. Receiver functions were calculated from the quiet... more
ABSTRACT We have used 4th root receiver function stacks, and pre-stack receiver function depth migrations to study the transition zone discontinuity structure beneath southwestern Japan. Receiver functions were calculated from the quiet short-period seismograms recorded by a recently deployed borehole network, Hi-net. We found that a relatively broad frequency band can be retrieved from a short-period seismogram by deconvolution of the instrument response. The quality of the receiver functions formed from large earthquake recordings is comparable to those from broadband instruments. We applied common-conversion-point gathering to the receiver-function data to image the P to S conversion events beneath the network by stacking with a 4th root technique to improve lateral coherence. We found that the topographic anomalies of the 410-km and 660-km discontinuities beneath southwest Japan have very different length scales. The former is characterized by a narrow, ~150-200 km wide, topographic high, while the latter exhibits a broad, >400 km wide, moderate topographic low together with a small-scale, larger-amplitude depression. A 2.5D pre-stack depth migration of the receiver functions shows the transition zone features clearly, as well as images a change of slope in the subducting slab at the 410-km discontinuity and flattening of the slab onto the 660-km discontinuity. These observations show that the subducted Pacific slab is deflected when it encounters the upper and lower boundaries of the transition zone, and is flat lying either above or across the 660-km discontinuity. The flat lying slab is, however, restricted to the bottom of the transition zone, and probably is much less thickened than is suggested by some global tomographic images in which subhorizontal high velocity anomalies are seen throughout the transition zone between the two discontinuities.
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We have made PdS receiver functions from USArray Transportable Array data to examine lithosphere and upper mantle structure beneath most of the tectonic western US. We present a CCP stacked volume of~ 10,000 receiver functions from 61... more
We have made PdS receiver functions from USArray Transportable Array data to examine lithosphere and upper mantle structure beneath most of the tectonic western US. We present a CCP stacked volume of~ 10,000 receiver functions from 61 events recorded at 520 stations. Receiver functions were formed both by spectral division with water level stabilization, and by using a time domain iterative deconvolution method. The data were depth converted, laterally repositioned, and CCP stacked using linear tomography ...
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Seismic tomography studies have revealed two broad slow shear-wave speed anomalies regions beneath the Pacific and Africa called as LLSVPs (Large Low Seismic Velocity Provinces). There are geographic correlations between the LLSVPs and... more
Seismic tomography studies have revealed two broad slow shear-wave speed anomalies regions beneath the Pacific and Africa called as LLSVPs (Large Low Seismic Velocity Provinces). There are geographic correlations between the LLSVPs and hotspots, and the LLSVPs could probably play an important role for convection throughout the mantle and thermal structure and evolution of the earth. The LLSVPs have been considered to be heterogeneous in composition since the boundaries between the normal mantle are sharp. To investigate the details of the sharp LLSVP edge we measure ScS–S and SKS–S differential traveltimes in the hypocentral distance of about 60 –90° using Japanese and Chinese seismic networks. We found anomalously large (more than 5 sec) ScS –S travel times accompanying normal SKS –S travel times, suggesting local strong slow region in the vicinity of the ScS bounce points (red circles in Figure 1). Such ScS bounce points locate to the northeast of New Guinea Island extending over ...
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Research Interests: Geology and Seismology
From 2011 to 2013, the CHINArray project led by the Institute of Geophysics, China Earthquake Administration, made the first phase deployment of 350 broadband seismometers at the southeastern margin of the Tibetan plateau. The... more
From 2011 to 2013, the CHINArray project led by the Institute of Geophysics, China Earthquake Administration, made the first phase deployment of 350 broadband seismometers at the southeastern margin of the Tibetan plateau. The three-component records of the CHINArray-I have been widely used in studying seismic structures beneath the margin under the assumption that the two horizontal components of seismometers are well aligned toward geographic north and east. In this study, we estimated the actual orientation of the two horizontal components of the 350 seismometers by analyzing P-wave particle motions of teleseismic earthquakes. Among the 350 stations, we found 80 stations were mildly misaligned by 5°–20°, and another 49 stations had misorientations larger than 20° or other malfunctioning issues. We also investigated how sensor misalignment affects seismic studies that rely on the vectorial nature of seismic recording, such as constructing receiver functions, estimating seismic ani...
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The southernmost edge of the Caribbean (CAR) plate, a buoyant large igneous province, subducts shallowly beneath northwestern South America (NWSA) at a trench that lies northwest of Colombia. Recent finite frequency P-wave tomography... more
The southernmost edge of the Caribbean (CAR) plate, a buoyant large igneous province, subducts shallowly beneath northwestern South America (NWSA) at a trench that lies northwest of Colombia. Recent finite frequency P-wave tomography results show a segmented CAR subducting at a shallow angle under the Santa Marta Massif to the Serrania de Perijá (SdP) before steepening while a detached segment beneath the Mérida Andes (MA) descends into the mantle transition zone. The dynamics of shallow subduction are poorly understood. Plate coupling between the flat subducting CAR and the overriding NWSA is proposed to have driven the uplift of the MA. In this study we analyze SKS shear wave splitting to investigate the seismic anisotropy beneath the slab segments to relate their geometry to mantle dynamics. We also use local S splitting to investigate the seismic anisotropy between the slab segments and the overriding plate. The data were recorded by a 65-element portable broadband seismograph n...
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Full waveform tomography is an effective method to obtain high‐resolution subsurface velocity structures. It is, however, difficult for the conventional L2‐norm‐based inversion to reach the global minimum because of cycle‐skipping... more
Full waveform tomography is an effective method to obtain high‐resolution subsurface velocity structures. It is, however, difficult for the conventional L2‐norm‐based inversion to reach the global minimum because of cycle‐skipping problem. In this study, we investigated the feasibility of using the quadratic Wasserstein metric distance (W2 norm) as the misfit function for passive adjoint tomography. We first derived equations of the Fréchet gradient and adjoint source under W2‐norm misfit function. We then conducted numerical experiments to illustrate the effectiveness of the proposed method in avoiding cycle skipping. We finally applied the adjoint tomography to eastern Tibet and obtained a 3‐D velocity model of the lithosphere. The adjoint tomography revealed two low‐velocity channels beneath the NE and SE margins of the Tibetan plateau, which were also observed by previous studies. Our results are consistent with the lower crust flow model that was proposed to explain the deforma...
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The dehydration of oceanic slabs during subduction is mainly thermally controlled and is often expressed as intermediate‐depth seismicity. In warm subduction zones, shallow dehydration can also lead to the buildup of pore‐fluid pressure... more
The dehydration of oceanic slabs during subduction is mainly thermally controlled and is often expressed as intermediate‐depth seismicity. In warm subduction zones, shallow dehydration can also lead to the buildup of pore‐fluid pressure near the plate interface, resulting in nonvolcanic tremor. Along the Cascadia margin, tremor density and intermediate‐depth seismicity correlate but vary significantly from south to north despite little variation in the thermal structure of the Juan de Fuca Plate. Along the northern and southern Cascadia margin, intermediate‐depth seismicity likely corresponds to increased fluid flux, while increased tremor density may result from fluid infiltration into thick underthrust metasediments characterized by very slow shear wave velocities (<3.2 km/s). In central Cascadia, low intermediate‐depth seismicity and tremor density may indicate a lower fluid flux, and shear wave velocities indicate that the Siletzia terrane extends to the plate interface. Thes...
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We utilized data from the BOLIVAR project and the permanent national seismic network of Venezuela to investigate the boundary between Venezuela and southeastern Caribbean. We made shear wave splitting measurements on SKS and SKKS phases... more
We utilized data from the BOLIVAR project and the permanent national seismic network of Venezuela to investigate the boundary between Venezuela and southeastern Caribbean. We made shear wave splitting measurements on SKS and SKKS phases using techniques developed by Silver and Chan (1991). We examined 3000+ station event pairs and found approximately 300 with visible SKS and/or SKKS phases. From
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Research Interests: Geology, Geophysics, China, Seismology, Volcano, and 4 moreGeomatic Engineering, Geophysical, Volcanism, and Attenuation
Research Interests: Geology and Tomography
We conducted delay time tomography of the upper mantle beneath the northwestern Pacific using P data from NorthEast China Extended SeiSmic Array, F‐net, and nearby available stations. To improve resolution and accuracy in the vicinity of... more
We conducted delay time tomography of the upper mantle beneath the northwestern Pacific using P data from NorthEast China Extended SeiSmic Array, F‐net, and nearby available stations. To improve resolution and accuracy in the vicinity of mantle discontinuities, we extracted traveltimes of both initial and secondary phases observed at triplication distances by using a waveform fitting technique. Compared with the model obtained by using only the initial phase, the resolution just above the 410 km discontinuity is especially improved, and low‐velocity anomalies beneath the Changbai Volcano are clearly observed down to the 410 km discontinuity. Compared with previous models, low‐velocity anomalies atop the 410 are more pronounced. The results of this study together with the previous receiver function analysis provide further support that we have hot material beneath the Changbai Volcano.
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Strong and localized seismic discontinuity and reflectors have been observed in the lower mantle at various depths beneath western Pacific subduction zones. The lateral extension of these anomalous structures, however, is not well... more
Strong and localized seismic discontinuity and reflectors have been observed in the lower mantle at various depths beneath western Pacific subduction zones. The lateral extension of these anomalous structures, however, is not well constrained. The information may hold the key to the understanding of the nature of these seismic structures as well as the related mantle processes. The USArray opens a new window for ``viewing'' and mapping these seismic anomalies. We found a clear later phase ~35-42 s after the direct P wave at most of the USArray recordings of two deep earthquakes that occurred near the border between east Russia and northeast China. The measured incident angle and arriving direction of this arrival suggest that it is an S to P wave converted at ~1000 km below Earth's surface. The mid-mantle discontinuity has a lateral dimension of greater than 200 km and 50 km along the EW and NS direction, respectively. It dips toward the east by ~12 degrees. The disco...