Research Highlights - University of Chinese Academy of Sciences)

Tectonophysics：The 2021 and 2022 Fukushima-Oki earthquake doublet: Reactivations of the bending-related faults inside the Japan Trench subducting slab -

2023-04-18T19:34:16+00:00

Abstract

The Pacific and Okhotsk plates are converging at a rate of about 9 cm/a, thereby forming the Japan Trench subduction zone. Two large earthquakes occurred in the offshore region of Fukushima on 13 February 2021 (M_w 7.1) and 16 March 2022 (M_w 7.3). The occurrences of the two earthquakes are close in space and time, thus constituting the Fukushima-Oki earthquake doublet. The joint inversions of the onshore and offshore strong-motion data and the teleseismic P waves reveal that both earthquakes belong to intraslab events, and the unilateral ruptures of the 2021 and 2022 events propagate southwestward and northeastward, respectively. Both events are dominated by thrust motions, and major fault slips are mainly localized away from the rupture initiating area. The geometries and locations of the two seismogenic faults suggest that the Fukushima-Oki doublet arises from the reactivations of two preexisting bending-related faults inside the subducting Pacific plate, which is driven by the downdip compressional stress regime caused by plate unbending. Furthermore, the regional tectonic settings indicate a complicated seismogenic environment for the Fukushima-Oki doublet, in which the dehydration embrittlement and seamount subduction are likely to play significant roles. Additionally, the distinctive rupture patterns of both events are also associated with the variation of fluid content and the small-scale structure of a slab slice enclosed by the two seismogenic faults within the subducting plate, which may control the heterogenous distributions of fault slips and aftershocks. The analysis of Coulomb failure stress changes suggests that the 2021 event and the 2022 foreshock collectively increase the stress loading, which may facilitate the occurrence of the 2022 mainshock, and the seismicity of the seismic belt consisting of the three intraslab sequences following the great 2011 Tohoku-Oki earthquake is also likely to remain active in the future.

Highlights

Source rupture processes of two Fukushima-Oki earthquakes in northeastern Japan.
Joint inversions of onshore and offshore strong-motion and teleseismic waveforms.
Two unilateral ruptures separately propagating southwestward and northeastward.
Both intraslab events caused by reactivations of preexisting outer-trench faults.
Seismogenesis attributed to heterogenous fluid content and regional tectonics.

https://doi.org/10.1016/j.tecto.2023.229800

PCM:First-principles study of high-pressure stability, structure, and elasticity of FeS2 polymorphs

2013-12-05T16:00:00+00:00

Abstract: The pressure-dependent elastic properties of the Fe–S system are important to understand the dynamic properties of the earth’s interior. We have therefore under-taken a first-principles study of the structural and elastic properties of FeS2 polymorphs under high pressure using a method based on plane-wave pseudopotential density function theory. The lattice constants, elastic constants, zero-pressure bulk modulus, and its pressure derivative of pyrite are in good agreement with the previous experiments and theoretical approaches; the lattice constants of marcasite are also consistent with the available experimental data. Calculations of the elastic constants of pyrite and marcasite have been determined from 0 to 200 gPa. Based on the relationship between the calculated elastic constants and the pressure, which can provide the stability of mineral, it would appear that pyrite is stable, whereas marcasite is unstable when the pressure rises above 130 gPa. Static lattice energy calculations predict the marcasite-to-pyrite phase transition to occur at 5.4 gPa at 0 K.

Citation: Shanqi Liu , Yongbing Li , Junli Yang , Huiquan Tian ,Bojing Zhu , Yaolin Shi . First-principles study of high-pressure stability, structure, and elasticity of FeS2 polymorphs. Phys Chem Minerals.

GRL: An experimental study of the inﬂuence of graphite on the electrical conductivity of olivine aggregates

2013-11-26T16:00:00+00:00

Abstract: Presence of graphite is one of the mechanisms to explain enhanced electrical conductivity. Because the conductivity of graphite is highly anisotropic and the connectivity of graphite depends strongly on the geometry of the crystals, the key issue is the geometry of graphite in a rock including their crystallographic orientation and the shape of graphite crystals. We explored the role of graphite on electrical conductivity in olivine-rich aggregates. To obtain well-deﬁned results, we conducted an experimental study at high pressure and temperature conditions. Olivine aggregates containing diamonds were annealed to transform diamond to graphite with nearly equilibrium morphology. Graphite formed by the transformation from diamond has thin disk-shape morphology, the plane being the highly conductive (0001) plane. When the concentration of graphite exceeds the percolation threshold (~ 1 wt%), electrical conductivity is signiﬁcantly enhanced. Some of the observed high conductivity regions may represent regions of high concentration of graphite.

Citation: Wang, D., S.-i. Karato, and Z. Jiang (2013), An experimental study of the inﬂuence of graphite on the electrical conductivity of olivine aggregates, Geophys. Res. Lett., 40, doi:10.1002/grl.50471.

PCM: Electrical conductivity of talc aggregates at 0.5 GPa: inﬂuence of dehydration

2013-11-26T16:00:00+00:00

Abstract: Electrical conductivity of talc was measured at 0.5 GPa and *473 to *1,300 K by using impedance spectroscopy both before and after dehydration. Before dehydration, the electrical conductivity of talc increased with temperature and is *10-4 S/m at 1,078 K. After dehydration, most of the talc changed to a mixture of enstatite and quartz and the total water content is reduced by a factor 6 or more. Despite this large reduction in the total water content, the electrical conductivity increased. The activation enthalpy of electrical conductivity (*125 kJ/mol) is too large for the conduction by free water but is consistent with conduction by small polaron. Our results show that a majority of hydrogen atoms in talc do not enhance electrical conductivity, implying the low mobility of the hydrogen atoms in talc. The observed small increase in conductivity after dehydration may be attributed to the increase in oxygen fugacity that enhances conductivity due to small polaron.

Citation: Duojun Wang , Shun-ichrio Karato. Electrical conductivity of talc aggregates at 0.5 GPa: inﬂuence of dehydration. Phys Chem Minerals (2013) 40:11–17, DOI 10.1007/s00269-012-0541-9

GJI: Relation of dislocation Love numbers and conventional Love numbers and corresponding Green’s functions for a surface rupture in a spherical earth model

2013-11-26T16:00:00+00:00

SUMMARY

This study was undertaken to complete the dislocation theory presented by Sun et al. for a spherical earth model with special treatment of coseismic deformations for a surface rupture. The previous theory is valid only for inner sources, but the coseismic deformations for a surface rupture source remain unsolved. Therefore, this study deals with the special case of coseismic deformations for a surface rupture dislocation. For this purpose, we ﬁrst derive the relation between the dislocation Love numbers and the conventional Love numbers, that is, the tidal, press, and shear Love numbers, based on the Okubo reciprocity theorem. Then we derive the corresponding Green’s functions for coseismic displacement, potential/geoid, gravity and strain changes using Okubo asymptotic solutions. Finally, we present numerical results of those Green’s functions for four independent seismic sources. Then we discuss the computation of coseismic deformations at the singular point—epicentre. As a case study, the computations of the coseismic deformations caused by the 2011 Tohoku-Oki earthquake (Mw 9.0) with considering the new Green’s functions as a constrain validates the theoretical model established in this study.

Citation: Wenke Sun and Jie Dong, Relation of dislocation Love numbers and conventional Love numbers and corresponding Green’s functions for a surface rupture in a spherical earth model , Geophysical Journal International, (2013) 193, 717–733

TAOS: A feasibility study of an FEM simulation used in co-seismic deformations: A case study of a dip-slip fault

2013-11-26T16:00:00+00:00

ABSTRACT

For this study, we conducted a numerical simulation on co-seismic displacement for a dip-slip fault in a half-space medium based upon a finite element method (FEM). After investigating technical problems of modeling, source and boundary treatment, we calculated co-seismic deformation with consideration to topography. To verify the numerical simulation results, the simulated co-seismic displacement was compared with that calculated using a dislocation theory. As a case study, considering the seismic parameters of the 2008 Wenchuan earthquake (M 8.0) as a source model, we calculate the co-seismic displacements with or without consideration of the terrain model in the finite element model to observe terrain effects on co-seismic deformation. Results show that topography has a non-negligible effect on co-seismic displacement, reaching from -11.59 to 4.0 cm in horizontal displacement, and from -3.28 to 3.28 cm in vertical displacement. The relative effects are 9.05 and 2.95% for horizontal and vertical displacement, respectively. Such a terrain effect is sufficiently large and can be detected by modern geodetic measurements such as GPS. Therefore, we conclude that the topography should be considered in applying dislocation theory to calculate co-seismic deformations.

Key words: Dislocation theory, FEM simulation, Double-node technique, Co-seismic displacement, Topographical effect

Citation: Lin, X., W. Sun, H. Zhang, X. Zhou, and Y. Shi, 2013: A feasibility study of an FEM simulation used in co-seismic deformations: A case study of a dip-slip fault. Terr. Atmos. Ocean. Sci., 24, 637-647, doi: 10.3319/TAO.2013.01.16.01(TibXS)

TAOS: Effects of huge earthquakes on Earth rotation and the length of day

2013-11-26T16:00:00+00:00

Abstract

We calculated the co-seismic Earth rotation changes for several typical great earthquakes since 1960 based on Dahlen’s analytical expression of Earth inertia moment change, the excitation functions of polar motion and, variation in the length of a day (ΔLOD). Then, we derived a mathematical relation between polar motion and earthquake parameters, to prove that the amplitude of polar motion is independent of longitude. Because the analytical expression of Dahlen’s theory is useful to theoretically estimate rotation changes by earthquakes having different seismic parameters, we show results for polar motion and ΔLOD for various types of earthquakes in a comprehensive manner. The modeled results show that the seismic effect on the Earth’s rotation decreases gradually with increased latitude if other parameters are unchanged. The Earth’s rotational change is symmetrical for a 45° dip angle and the maximum changes appear at the equator and poles. Earthquakes at a medium dip angle and low latitudes produce large rotation changes. As an example, we calculate the polar motion and ΔLOD caused by the 2011 Tohoku-Oki Earthquake using two different fault models. Results show that a fine slip fault model is useful to compute co-seismic Earth rotation change. The obtained results indicate Dahlen’s method gives good approximations for computation of co-seismic rotation changes, but there are some differences if one considers detailed fault slip distributions. Finally we analyze and discuss the co-seismic Earth rotation change signal using GRACE data, showing that such a signal is hard to be detected at present, but it might be detected under some conditions. Numerical results of this study will serve as a good indicator to check if satellite observations such as GRACE can detect a seismic rotation change when a great earthquake occur.

Key words: Earth rotation, Earthquake, Polar motion, Change in length of day

Citation: Xu, C., W. Sun, and X. Zhou, 2013: Effects of huge earthquakes on Earth rotation and the length of day. Terr. Atmos. Ocean. Sci., 24, 649-656, doi

PR: Precambrian Crustal Evolution of the Eastern North China Craton as Revealed by U-Pb Ages and Hf Isotopes of Detrital Zircons from the Proterozoic Jing' Eryu Formation

2012-04-26T16:00:00+00:00

Citation: Sun, J.F., Yang, J.H., Wu, F.Y., Wilde, S.A., 2012. Precambrian crustal evolution of the eastern North China Craton as revealed by U-Pb ages and Hf isotopes of detrital zircons from the Proterozoic Jing’eryu Formation. Precambrian Research, 200-203: 184-208.

Abstract: Simultaneous in situ U-Pb dating, trace element and Hf isotopic analyses have been carried out on detrital zircons obtained from sandstones in the Neoproterozoic Jing’eryu Formation from the Eastern block, North China Craton (NCC), with the aim of constraining the ages of magmatic and metamorphic events and Precambrian crustal evolution of the NCC. Two groups of zircons, i.e., magmatic and metamorphic in origin, have been identified based on cathodoluminescence images, zircon Ti-temperatures and Th/U ratios. Zircon U-Pb dating shows two main magmatic events with ages of 2.55-2.47 Ga and 1.80-1.70 Ga, and four metamorphic events, with ages of 2.51-2.48 Ga, 1.96-1.90 Ga, 1.87-1.85 Ga and ~1.80 Ga in the NCC. No zircon with an age more than 3.8 Ga has been identified in this study, indicating the limited presence of 3.8 Ga rocks in the NCC.

The Hf isotopic data show the ~2.5 Ga magmatic zircons have variable Hf(t) values with crustal model ages of 2.7-2.9 Ga, which can be interpreted to indicate mixed sources for their parental rocks, i.e., ancient crust (3.8 Ga or 3.3 Ga) and depleted mantle, implying significant continental crustal growth at ~2.5 Ga. However, Paleoproterozoic magmatic zircons all have negative εHf(t) and Archean Hf model ages, suggesting that their parental rocks were formed by recycled Archean materials.

The widespread ~2.5 Ga metamorphism in the Eastern Block, coupled with extensive ~2.5 Ga magmatism and crustal growth, are consistent with a mantle plume beneath the Eastern Block of the NCC during Neoarchean. whereas, belt-like ~1.85 Ga metamorphism, i.e., the increase of the metamorphic zircons with Paleoproterozoic ages from the Eastern Block to the Trans-North China orogen, is possibly explained by assembly between Eastern and Western Blocks at Paleoproterozoic.

PPP: Magnetostratigraphic Dating of the Xiashagou Fauna and Implication for Sequencing the Mammalian Faunas in the Nihewan Basin, North China

2012-04-26T16:00:00+00:00

Citation: Liu Ping, Deng Chenglong, Li Shihu, Cai Shuhui, Cheng Hongjiang, Yuan Baoyin, Wei Qi, Zhu Rixiang. Magnetostratigraphic dating of the Xiashagou Fauna and implication for sequencing the mammalian faunas in the Nihewan Basin, North China. Palaeogeography, Palaeoclimatology, Palaeoecology, 2012, 315-316: 75-85.

Abstrct:The Nihewan Basin sedimentary sequences in northern China are rich in mammalian fossil and Paleolithic sites, thus providing insights into our understanding of Quaternary land mammal biochronology and early human settlements in East Asia. Here we present high resolution magnetostratigraphic results that place stringent age controls on the Xiashagou (XSG) Fauna (that is, the well-known Nihewan Fauna sensu stricto) in the Nihewan Basin, northern China. Results show that the XSG sequence recorded the Brunhes normal chron, the Matuyama reverse chron and the late Gauss normal chron. The XSG Fauna resides in the Matuyama reverse chron (between the pre-Reunion Matuyama chron and the post-Olduvai Matuyama chron), yielding an estimated age of ca. 2.2–1.7 Ma. The Pliocene–Pleistocene boundary (Gauss/Matuyama boundary) is located in the lower part of the XSG section. The combination of our study and previously published magnetostratigraphic data suggest that the mammalian fossil sites in the eastern Nihewan Basin can be placed between the Gauss–Matuyama geomagnetic reversal and the Matuyama–Brunhes geomagnetic reversal (2.58–0.78 Ma), leading to a time range of ca. 2.6–0.8 Ma for the Nihewan mammalian faunas.

ACP: Five-year Record of Atmospheric Precipitation Chemistry in Urban Beijing, China.

2012-04-11T16:00:00+00:00

Citation:Yang F., Tan J., Shi Z., Cai Y., He K., Ma Y., Duan F., Okuda T., Tanaka S., and Chen G., Five-year record of atmospheric precipitation chemistry in urban Beijing, China. Atmospheric Chemistry and Physics, 2012, 12, 2025–2035, doi:10.5194/acp-12-2025-2012. (IF 5.309)

Abstract:To investigate the chemical characteristics of precipitation in the polluted urban atmosphere in Beijing and possible mechanisms influencing their variations, a total of 131 event-based precipitation samples were collected from March 2001 to August 2005. The concentrations of major ions in the samples were analyzed by using ion chromatography. Intermediate pH (6.1–7.3) was recorded in approximately two-thirds of the precipitation samples and acidic pH (4.2–5.6) in only 16% of the samples. However, the precipitation acidity was on the growth track and the process was likely being accelerated. SO2−4 , NO− 3 , NH+ 4 , and Ca2+ were the most abundant ions in the precipitations, with their single volume-weighted mean (VWM) concentration all above 100 μeq l−1. The two major anions and two major cations accounted for more than 80% of total anionic and cationic mass, respectively. The VWM SO2− 4 concentration decreased by 13% compared to that during 1995– 1998, much less than the 58% reduction in the annual average SO2 concentration from 1998 to 2005 in Beijing. What seems more counterintuitive is that the VWM NO− 3 concentration nearly doubled over the period although the annual average NO2 concentration decreased by 5% from 1998 to 2005. These results imply that the conversion of gaseous precursors to acid compounds and/or the regional transport were reinforced over the decade. The average ratio of neutralizing potential to acidifying potential (i.e. NP/AP) was as high as 1.2 but experienced an evident decline trend. This was mainly ascribed to reduced input of NH+ 4 and Ca2+ and increased input of NO− 3 . Furthermore, the equivalent mass ratio of NO− 3 to non-sea-salt SO2− 4 presented an increasing trend over the study period, suggesting that the contribution of NO− 3 to the precipitation acidity increased in recent years. However, the mean ratio was only 0.37±0.11 in the study period, which is significantly lower than those reported in some metropolitan areas in developed countries. This shows that the precipitation acidity in Beijing was still dominantly from SO2 while the SO2 contribution was progressively substituted by NOx.