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ISSN  2096-3955

CN  10-1502/P

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Arctic ozone loss in early spring and its impact on the stratosphere-troposphere coupling
ShuYang Yu, Jian Rao, Dong Guo
Recently Published, doi: 10.26464/epp2022015
[Abstract](222) [FullText HTML](3) [PDF 9963KB](6)
The tropospheric impact of Arctic ozone loss events is still debatable. In this study we investigate that question, using the ERA5 reanalysis and long-term integration by a climate-chemistry coupled model (CESM2-WACCM). We begin with the frequency of Arctic ozone loss events. On average, such events occur once in early spring every 14−15 years in ERA5 data and in the model, both of which estimate that roughly 40% of the strong polar vortex events in March are coupled with Arctic ozone loss, the remaining 60% being uncoupled. The composite difference between the two samples might be attributed to the pure impact of the Arctic ozone loss — that is, to ozone loss alone, without the concurrent impact of strong polar vortices. Arctic ozone loss is accompanied by an increase in total ozone in midlatitudes, with the maximum centered in the Central North Pacific. Contrasting Arctic ozone loss events with pure strong polar vortex events that are uncoupled with ozone loss, observations confirm that the stratospheric Northern Annular Mode reverses earlier for the former. For pure strong vortex events in early spring (without Arctic ozone loss), the cold anomalies can extend from the stratosphere to the middle troposphere; when such events are strong, the near surface warm anomalies are biased toward the continents. In contrast, during the other 40% of strong early-spring polar vortex events, those coupled with ozone loss, a concurrent and delayed warming of the near surface over the Arctic and its neighboring areas is observed, due to vertical redistribution of solar radiation by the change in the ozone.
The 600 keV electron injections in the Earth’s outer radiation belt: A statistical study
ChaoLing Tang, Xu Wang, BinBin Ni, ZhengPeng Su, JiChun Zhang
Recently Published, doi: 10.26464/epp2022012
[Abstract](393) [FullText HTML](7) [PDF 2257KB](9)
Relativistic electron injections are one of the mechanisms of relativistic (≥0.5 MeV) electron enhancements in the Earth’s outer radiation belt. In this study, we present a statistical observation of 600 keV electron injections in the outer radiation belt by using data from the Van Allen Probes. On the basis of the characteristics of different injections, 600 keV electron injections in the outer radiation belt were divided into pulsed electron injections and nonpulsed electron injections. The 600 keV electron injections were observed at 4.5 < L < 6.4 under the geomagnetic conditions of 450 nT < AE < 1,450 nT. An L of ~4.5 is an inward limit for 600 keV electron injections. Before the electron injections, a flux negative L shell gradient for ≤0.6 MeV electrons or low electron fluxes in the injected region were observed. For 600 keV electron injections at different L shells, the source populations from the Earth’s plasma sheet were different. For 600 keV electron injections at higher L shells, the source populations were higher energy electrons (~200 keV at X ~ –9 RE), whereas the source populations for 600 keV electron injections at lower L shells were lower energy electrons (~80 keV at X ~ –9 RE). These results are important to further our understanding of electron injections and rapid enhancements of 600 keV electrons in the Earth’s outer radiation belt.
Modeling of kilometer-scale ionospheric irregularities at Mars
ChunHua Jiang, Rong Tian, LeHui Wei, GuoBin Yang, ZhengYu Zhao
Recently Published, doi: 10.26464/epp2022011
[Abstract](425) [FullText HTML](9) [PDF 427KB](5)
Recently, kilometer-scale Martian ionospheric irregularities have been measured by the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission (Fowler et al., 2020). In this study, we carried out a simulation of these irregularities, assuming a uniform Martian zonal neutral wind and a cosinusoidal perturbation of the plasma density as the seeding source. Results show that a vertical electric field shear could be induced by such a plasma density perturbation. We find that the vertical electric field shear causes a velocity shear of the plasma between the topside and bottomside ionosphere, which in turn is able to produce kilometer-scale ionospheric irregularities — irregularities of a smaller scale than were seen in previous simulations (Jiang CH et al., 2021). These kilometer-scale variations with altitude, in plasma density and magnetic field profiles, are comparable to the MAVEN observations.
Shallow crustal velocity structures revealed by active source tomography and fault activities of the Mianning–Xichang segment of the Anninghe fault zone, Southwest China
XiHui Shao, HuaJian Yao, Ying Liu, HongFeng Yang, BaoFeng Tian, LiHua Fang
Recently Published, doi: 10.26464/epp2022010
[Abstract](443) [FullText HTML](7) [PDF 1773KB](17)
The Anninghe fault is a large left-lateral strike-slip fault in southwestern China. It has controlled deposition and magmatic activities since the Proterozoic, and seismic activity occurs frequently. The Mianning−Xichang segment of the Anninghe fault is a seismic gap that has been locked by high stress. Many studies suggest that this segment has great potential for large earthquakes (magnitude >7). We obtained three vertical velocity profiles of the Anninghe fault (between Mianning and Xichang) based on the inversion of P-wave first arrival times. The travel time data were picked from seismograms generated by methane gaseous sources and recorded by three linearly distributed across-fault dense arrays. The inversion results show that the P-wave velocity structures at depths of 0−2 km corresponds well with the local lithology. The Quaternary sediments have low seismic velocities, whereas the igneous rocks, metamorphic rocks, and bedrock have high seismic velocities. We then further discuss the fault activities of the two fault branches of the Anninghe fault in the study region based on small earthquakes (magnitudes between \begin{document}$ {M}_{L} $\end{document} 0.5 and \begin{document}$ {M}_{L} $\end{document} 2.5) detected by the Xichang array. The eastern fault branch is more active than the western branch and that the fault activities in the eastern branch are different in the northern and southern segments at the border of 28°21′N. The high-resolution models obtained are essential for future earthquake rupture simulations and hazard assessments of the Anninghe fault zone. Future studies of velocity models at greater depths may further explain the complex fault activities in the study region.
Numerical modeling of metamorphic core complex formation: Implications for the destruction of the North China Craton
ZiQi Ma, Gang Lu, JianFeng Yang, Liang Zhao
Recently Published, doi: 10.26464/epp2022016
[Abstract](178) [FullText HTML](3) [PDF 2161KB](1)
Widespread magmatism, metamorphic core complexes (MCCs), and significant lithospheric thinning occurred during the Mesozoic in the North China Craton (NCC). It has been suggested that the coeval exhumation of MCCs with uniform northwest-southeast shear senses and magmatism probably resulted from a decratonization event during the retreat of the paleo-Pacific Plate. Here we used two-dimensional finite element thermomechanical numerical models to investigate critical parameters controlling the formation of MCCs under far-field extensional stress. We observed three end-member deformation modes: the MCC mode, the symmetric-dome mode, and the pure-shear mode. The MCC mode requires a Moho temperature of ≥700 °C and an extensional strain rate of ≥5 × 10−16 s−1, implying that the lithosphere had already thinned when the MCC was formed in the Mesozoic. Considering that the widespread MCCs have the same northwest-southeast extension direction in the NCC, we suggest that the MCCs are surface expressions of both large-scale extension and craton destruction and that rollback of the paleo-Pacific slab might be the common driving force.
Observation evidence for the entropy switch model of substorm onset
YunXiang Song, ChuXin Chen
Recently Published, doi: 10.26464/epp2022020
[Abstract](94) [FullText HTML](1) [PDF 856KB](2)
The cause of substorm onset is not yet understood. Chen CX (2016) proposed an entropy switch model, in which substorm onset results from the development of interchange instability. In this study, we sought observational evidence for this model by using Time History of Events and Macroscale Interactions during Substorms (THEMIS) data. We examined two events, one with and the other without a streamer before substorm onset. In contrast to the stable magnetosphere, where the total magnetic field strength is a decreasing function and entropy is an increasing function of the downtail distance, in both events the total magnetic field strength and entropy were reversed before substorm onset. After onset, the total magnetic field strength, entropy, and other plasma quantities fluctuated. In addition, a statistical study was performed. By confining the events with THEMIS satellites located in the downtail region between ~8 and ~12 Earth radii, and 3 hours before and after midnight, we found the occurrence rate of the total magnetic field strength reversal to be 69% and the occurrence rate of entropy reversal to be 77% of the total 205 events.
Inter-annual variations of 6.5-day planetary waves and their relations with QBO
YingYing Huang, Jun Cui, HuiJun Li, ChongYin Li
Recently Published, doi: 10.26464/epp2022005
[Abstract](622) [FullText HTML](7) [PDF 17776KB](25)
This paper studies inter-annual variations of 6.5-Day Waves (6.5DWs) observed at altitudes 20−110 km between 52°S−52°N latitudes during March 2002−January 2021, and how these variations were related to the equatorial stratospheric Quasi-Biennial Oscillation (QBO). Temperature amplitudes of the 6.5DWs are calculated based on SABER/TIMED observations. QBO zonal winds are obtained from an ERA5 reanalysis dataset. QBO phases are derived using an Empirical Orthogonal Functions (EOF) method. Wavelet analysis of the observed 6.5DW variations demonstrates obvious spectral maximums around 28−38 months at 32°N−52°N, and around 26−30 months at 32°S−52°S. In the Northern Hemisphere, peak periods lengthened poleward; in the Southern Hemisphere, however, they were unchanged with latitude. Residual 6.5DWs amplitudes have been determined by removing composite amplitudes from 6.5DWs amplitudes. Comparisons between QBO and monthly maximum residual 6.5DWs amplitudes (\begin{document}$ {A}_{\mathrm{M}\mathrm{m}\mathrm{a}\mathrm{x}} $\end{document}) show clear correlations between the QBO and 6.5DWs in both hemispheres, but the observed relationship is stronger in the NH. When \begin{document}$ {A}_{\mathrm{M}\mathrm{m}\mathrm{a}\mathrm{x}} $\end{document} were large in the NH, the mean QBO profile was easterly at all levels from 70 to 5 hPa; when the \begin{document}$ {A}_{\mathrm{M}\mathrm{m}\mathrm{a}\mathrm{x}} $\end{document} were weak, the mean QBO wind was weak westerly below 30 hPa. Linear Pearson correlation coefficients between QBO phases and \begin{document}$ {A}_{\mathrm{M}\mathrm{m}\mathrm{a}\mathrm{x}} $\end{document} show large positive values at 60−110 km between 20°N−52°N in April and around 64 km at 24°S in February, and large negative values from 80 to 110 km between 20°N−50°N in August and at 96−106 km between 20°S−44°S in February. These results indicate quantitative correlations between QBO and 6.5DWs and provide credible evidences for further studies of QBO modulations on long-term variations of 6.5DWs.


Runoff Variations in the Yangtze River Basin and Sub-basins based on GRACE, Hydrological models, and In-situ data
WeiLong Rao, WenKe Sun
Accepted Articles, doi: 10.26464/epp2022021
[Abstract](25) [PDF](0)
Water budget closure is a method to study the balance of basin water storage and the dynamics of hydrological components (e.g., precipitation, evapotranspiration, and runoff). When the water budget closure is connected with terrestrial water storage change (TWSC) estimated from the Gravity Recovery and Climate Experiment (GRACE) data, the variations in the basin runoff can be well researched. In this study, the total runoff variations in the Yangtze River Basin (YRB) and its sub-basins are studied in detail based on the water budget closure equation. The mainstream precipitation and evapotranspiration models were compared and combined to determine the interval of precipitation minus evapotranspiration. In addition, generally neglected human water consumption is discussed and considered here. The final estimated runoff variations in the YRB and its sub-basins were compared with in-situ discharge variations to evaluate the application effect of these hydrological models and estimate the subsurface runoff. The estimated runoff variations show that runoff over the YRB showed an increasing trend, especially in the lower sub-basins and in the post-monsoon season, accompanied by apparent terrestrial water loss.

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Tianwen-1 MINPA observations in the solar wind
AiBing Zhang, LingGao Kong, WenYa Li, Lei Li, BinBin Tang, ZhaoJin Rong, Yong Wei, JiJie Ma, YiTeng Zhang, LiangHai Xie, YuXian Wang, JianSen He, Bin Liu, WenJing Wang, Bin Su, JiaWei Li, Xu Tan, Fang Wang, TaiFeng Jin, FuHao Qiao, Peter Wurz, Yan Zhu, YunFei Bai, YiRen Li, XinBo Zhu, YueQiang Sun, YongLiao Zou, Chi Wang
2022, 6(1): 1 -9. doi: 10.26464/epp2022014
The Mars Ion and Neutral Particle Analyzer (MINPA) is one of the three scientific instruments onboard the Tianwen-1 orbiter to investigate the Martian space environment. During Tianwen-1’s transfer orbit to Mars, the MINPA was switched on to measure the solar wind ions. Here, we present the first results of the MINPA observations in the solar wind. During cruise, nearly half of the MINPA ion field-of-view (FOV) was blocked by the lander capsule; thus only the solar-wind ions with azimuthal speeds pointing towards the unblocked FOV sectors could be detected. We perform a detailed comparison of the MINPA’s solar wind observations with data from Earth-based missions when MINPA reached its count-rate peak, finding a general consistency of the ion moments between them. The blocking effect due to the lander is evaluated quantitatively under varying solar-wind velocity conditions. Despite the blocking effect, the MINPA’s solar wind measurements during the transfer orbit suggest a good performance.
Comment on “Locating the source field lines of Jovian decametric radio emissions” by YuMing Wang et al.
Laurent Lamy, Baptiste Cecconi, Stéphane Aicardi, C. K. Louis
2022, 6(1): 10 -12. doi: 10.26464/epp2022018
In this comment on the article “Locating the source field lines of Jovian decametric radio emissions” by Wang YM et al., 2020, we discuss the assumptions used by the authors to compute the beaming angle of Jupiter’s decametric emissions induced by the moon Io. Their method, relying on multi-point radio observations, was applied to a single event observed on 14th March 2014 by Wind and both STEREO A/B spacecraft from ~5 to ~16 MHz. They have erroneously identified the emission as a northern (Io-B type) instead of a southern one (Io-D type). We encourage the authors to update their results with the correct hemisphere of origin and to test their method on a larger sample of Jupiter-Io emissions.
Reply to Comment by Lamy et al. on “Locating the source field lines of Jovian decametric radio emissions”
YuMing Wang, RuoBing Zheng, XianZhe Jia, ChuanBing Wang, Shui Wang, V. Krupar
2022, 6(1): 13 -17. doi: 10.26464/epp2022019
Locating the source of decametric (DAM) radio emissions is a key step in the use of remote radio observations to understand the Jovian magnetospheric dynamics and their interaction with the planet’s moons. Wang YM et al. (2020) presented a method by which recorded arc-shaped DAM emissions in the radio dynamic spectra can be used to locate the source of a DAM. An Io-related DAM event on March 14, 2014 was used to demonstrate the method. A key parameter in the method is whether the DAM is emitted in the northern or the southern hemisphere; the hemisphere of origin can be determined definitively from the polarization of the emission. Unfortunately, polarization information for the emission on March 14, 2014 event was not recorded. Our analysis assumed the source to be in the northern hemisphere. Lamy et al. (2022) argue convincingly that the source was probably in the southern hemisphere. We appreciate the helpful contribution of Lamy et al. (2022) to this discussion and have updated our analysis, this time assuming that the DAM source was in the southern hemisphere. We also explore the sensitivity of our method to another parameter — the height at which the value of fce,max, which is the maximal electron cyclotron frequency reached along the active magnetic flux tube, is adopted. Finally, we introduce our recent statistical study of 68 DAM events, which lays a more solid basis for testing the reliability of our method, which we continue to suggest is a promising tool by which remote radio observations can be used to locate the emission source of Jovian DAMs.
Thermal inertia at the MSL and InSight mission sites on Mars
D. Singh, S. Uttam
2022, 6(1): 18 -27. doi: 10.26464/epp2022004
For planetary surface materials, thermal inertia is the critical property that governs the surface’s daily thermal response and controls diurnal and seasonal surface temperature variations. Here we use the ground measurements made by the MSL Curiosity rover and the InSight lander to determine the thermal inertia of two sites on Mars. This study compares the variation of thermal inertia during and after the Large Dust Storm (LDS) of Martian Year (MY) 34. To determine surface thermal inertia, we derive a simple approximation (using energy balance), which utilizes surface albedo, surface energy flux, and diurnal change in the surface temperature. The average thermal inertia in MY34 is about 39.2%, 3.7%, and 3.4% higher than MY35 average thermal inertia for the MSL, InSight (FOV1), and InSight (FOV2), respectively. Notably, the thermal inertia at the InSight (FOV1) is consistently lower by about 20 J·m–2·s–1/2·K–1 than the InSight (FOV2) site for all scenarios, indicating variation in the region’s surface composition. The best-fit surface albedo in MY34 (determined using the KRC model) are about 0.08, 0.05, and 0.03 higher than MY35 surface albedo for the MSL, InSight (FOV1), and InSight (FOV2), respectively. An increase in both surface albedo and thermal inertia during the LDS indicates that the underlying surface is both more thermally resistant and more reflective than the overlying loose dust.
Study of fluctuations in the Martian magnetosheath using a kurtosis technique: Mars Express observations
A. M. S. Franco, E. Echer, M. J. A. Bolzan, M. Fraenz
2022, 6(1): 28 -41. doi: 10.26464/epp2022006
Planetary magnetosheaths are characterized by high plasma wave and turbulence activity. The Martian magnetosheath is no exception; both upstream and locally generated plasma waves have been observed in the region between its bow shock and magnetic boundary layer, its induced magnetosphere. This statistical study of wave activity in the Martian magnetosheath is based on 12 years (2005–2016) of observations made during Mars Express (MEX) crossings of the planet’s magnetosheath — in particular, data on electron density and temperature data collected by the electron spectrometer (ELS) of the plasma analyzer (ASPERA-3) experiment on board the MEX spacecraft. A kurtosis parameter has been calculated for these plasma parameters. This value indicates intermittent behavior in the data when it is higher than 3 (the value for a normal or Gaussian distribution). The variation of wave activity occurrence has been analyzed in relation to solar cycle, Martian orbit, and distance to the bow shock. Non-Gaussian properties are observed in the magnetosheath of Mars on all analyzed scales, especially in those near the proton gyrofrequency in the upstream region of the Martian magnetosphere. We also report that non-Gaussian behavior is most prominent at the smaller scales (higher frequencies). A significant influence of the solar cycle was also observed; the kurtosis parameter is higher during declining and solar maximum phases, when the presence of disturbed solar wind conditions, caused by large scale solar wind structures, increases. The kurtosis decreases with increasing distance from the bow shock, which indicates that the intermittence level is higher near the bow shock. In the electron temperature data the kurtosis is higher near the perihelion due to the higher incidence of EUV when the planet is closer to the Sun, which causes a more extended exosphere, and consequently increases the wave activity in the magnetosheath and its upstream region. The extended exosphere seems to play a lower effect in the electron density data.
Neutralized solar energetic particles for SEP forecasting: Feasibility study of an innovative technique for space weather applications
Xiao-Dong Wang, B. Klecker, G. Nicolaou, S. Barabash, M. Wieser, P. Wurz, A. Galli, F. Cipriani, Y. Futaana
2022, 6(1): 42 -51. doi: 10.26464/epp2022003
Energetic neutral atoms (ENAs) are produced by the neutralization of energetic ions formed by shock-accelerated gradual solar energetic particle events (SEP). These high-energy ENAs (HENAs) can reach the Earth earlier than the associated SEPs and thus can provide information about the SEPs at the lower corona. The HENA properties observed at Earth depend on the properties of the coronal mass ejection (CME)-driven shocks that accelerate the SEPs. Using a model of HENA production in a shock-accelerated SEP event, we semi-quantitatively investigate the energy-time spectrum of HENAs depending on the width, propagation speed, and direction of the shock, as well as the density and ion abundances of the lower corona. Compared to the baseline model parameters, the cases with a wider shock width angle or a higher coronal density would increase the HENA flux observed at the Earth, while the case with an Earth-propagating shock shows a softened HENA spectrum. The comparison of expected HENA fluxes in different cases with a flight-proven ENA instrument suggests that solar HENAs can feasibly be monitored with current technologies, which could provide a lead time of 2−3 hours for SEPs at a few MeV. We propose that monitoring of solar HENAs could provide a new method to forecast shock-driven SEP events that are capable of significant space weather impacts on the near-Earth environment.
Automatic calculation of the magnetometer zero offset using the interplanetary magnetic field based on the Wang–Pan method
XiaoWen Hu, GuoQiang Wang, ZongHao Pan
2022, 6(1): 52 -60. doi: 10.26464/epp2022017
The space-borne fluxgate magnetometer (FGM) requires regular in-flight calibration to obtain its zero offset. Recently, Wang GQ and Pan ZH (2021a) developed a new method for the zero offset calibration based on the properties of Alfvén waves. They found that an optimal offset line (OOL) exists in the offset cube for a pure Alfvén wave and that the zero offset can be determined by the intersection of at least two nonparallel OOLs. Because no pure Alfvén waves exist in the interplanetary magnetic field, calculation of the zero offset relies on the selection of highly Alfvénic fluctuation events. Here, we propose an automatic procedure to find highly Alfvénic fluctuations in the solar wind and calculate the zero offset. This procedure includes three parts: (1) selecting potential Alfvénic fluctuation events, (2) obtaining the OOL, and (3) determining the zero offset. We tested our automatic procedure by applying it to the magnetic field data measured by the FGM onboard the Venus Express. The tests revealed that our automatic procedure was able to achieve results as good as those determined by the Davis–Smith method. One advantage of our procedure is that the selection criteria and the process for selecting the highly Alfvénic fluctuation events are simpler. Our automatic procedure could also be applied to find fluctuation events for the Davis–Smith method.
Analysis of inversion error characteristics of stellar occultation simulation data
MingChen Sun, QingLin Zhu, Xiang Dong, JiaJi Wu
2022, 6(1): 61 -69. doi: 10.26464/epp2022013
Atmospheric stellar occultation observation technology is an advanced space-based detection technology that can measure the vertical distribution of trace gas composition, temperature, and aerosol content in a planet’s atmosphere. In this study, an inversion algorithm of the onion-peeling method was constructed to invert the transmittance obtained from the forward mask. The method used a three-dimensional ray-tracing simulation to obtain the transmission path of the light in the Earth’s atmosphere. The relevant parameters were then combined in the high-resolution transmission molecular absorption (HITRAN) database, and line-by-line integration was performed to calculate the atmospheric transmittance. The transmittance value was then used as an input to calculate the vertical distribution of oxygen molecules when using the single-wavelength inversion of the onion-peeling method. Finally, the oxygen molecule content was compared with the value attained by the Mass Spectrometer and Incoherent Scatter Radar Extended (MSISE00) atmospheric model to determine the relative error of our model. The maximum error was found to be 0.3%, which is low enough to verify the reliability of our algorithm. Using Global-scale Observations of the Limb and Disk (GOLD) measured data to invert the oxygen number density, we calculated its relative deviation from the published result to further verify the algorithm. The inversion result was affected by factors such as prior data, the absorption spectral line type, the ellipticity of the Earth, and the accuracy of the orbit. Analysis of these error-influencing factors showed that the seasons and the Earth’s ellipticity affected the accuracy of the model only 0.001% and could therefore be ignored. However, latitude and solar activity had a greater impact on accuracy, on the order of 0.1%. The absorption line type affected the accuracy of the model by as much as 1%. All three of these factors therefore need to be considered during the inversion process.
Application of deep learning to estimate stratospheric gravity wave potential energy
Yue Wu, Zheng Sheng, XinJie Zuo
2022, 6(1): 70 -82. doi: 10.26464/epp2022002
One of the most important dynamic processes in the middle and upper atmosphere, gravity waves (GWs) play a key role in determining global atmospheric circulation. Gravity wave potential energy (GW Ep) is an important parameter that characterizes GW intensity, so it is critical to understand its global distribution. In this paper, a deep learning algorithm (DeepLab V3+) is used to estimate the stratospheric GW Ep. The deep learning model inputs are ERA5 reanalysis datasets and GMTED2010 terrain data. GW Ep averaged over 20−30 km from 60°S−60°N, calculated by COSMIC radio occultation (RO) data, is used as the measured value corresponding to the model output. The results show that (1) this method can effectively estimate the zonal trend of GW Ep. However, the errors between the estimated and measured value of Ep are larger in low-latitude regions than in mid-latitude regions, possibly due to the large number of convolution operations used in the deep learning model. Additionally, the measured Ep has errors associated with interpolation to the grid; this tends to be amplified in low-latitude regions because the GW Ep is larger and the RO data are relatively sparse, affecting the training accuracy. (2) The estimated Ep shows seasonal variations, which are stronger in the winter hemisphere and weaker in the summer hemisphere. (3) The effect of quasi-biennial oscillation (QBO) can be clearly observed in the monthly variation of estimated GW Ep, and its QBO amplitude may be less than that of the measured Ep.
A new approach for inversion of receiver function for crustal structure in the depth domain
TianYu Zheng, YuMei He, Yue Zhu
2022, 6(1): 83 -95. doi: 10.26464/epp2022008
A method for reconstructing crustal velocity structure using the optimization of stacking receiver function amplitude in the depth domain, named common conversion amplitude (CCA) inversion, is presented. The conversion amplitude in the depth domain, which represents the impedance change in the medium, is obtained by assigning the receiver function amplitude to the corresponding conversion position where the P-to-S conversion occurred. Utilizing the conversion amplitude variation with depth as an optimization objective, imposing reliable prior constraints on the structural model frame and velocity range, and adopting a stepwise search inversion technique, this method efficiently weakens the tendency of easily falling into the local extremum in conventional receiver function inversion. Synthetic tests show that the CCA inversion can reconstruct complex crustal velocity structures well and is especially suitable for revealing crustal evolution by estimating diverse velocity distributions. Its performance in reconstructing crustal structure is superior to that of the conventional receiver function imaging method.
Spatial distribution characteristics and mechanism of nonhydrological time-variable gravity in China contient
Yue Shen, QiuYu Wang, WeiLong Rao, WenKe Sun
2022, 6(1): 96 -107. doi: 10.26464/epp2022009
The purpose of this study is to explore nonhydrological mass transfer in China contient. For this purpose, gravity recovery and climate experiment (GRACE) data were obtained to study the spatial distribution of time variant gravity signals in China contient. Then, from auxiliary hydrological data processed according to the current hydrological model, a new more comprehensive hydrological model of China contient was constructed. Finally, the time variant signals of this new hydrological model were removed from the time variant gravity field computed from GRACE data, thus obtaining a description of the nonhydrological mass transfer of China contient. The physical sources and mechanisms of the resulting mass transfer are then discussed. The improved, more realistic, hydrological model used here was created by selecting the hydrological components with the best correlations in existing hydrological models, by use of correlation calculation, analysis, and comparison. This improved model includes water in soils and deeper strata, in the vegetation canopy, in lakes, snow, and glaciers, and in other water components (mainly reservoir storage, swamps, and rivers). The spatial distribution of the transfer signals due to nonhydrological mass in China contient was obtained by subtracting the combined hydrological model from the GRACE time-variable gravity field. The results show that the nonhydrological signals in China contient collected in GRACE data were mainly positive signals, and were distributed in the Bohai Rim and the northern and eastern parts of the Tibetan Plateau. The above nonhydrological mass transfer signals have been studied further and are discussed. The results show that the nonhydrological mass migration signals in the Bohai Rim region originate primarily from sea level change and marine sediment accumulation. The mass accumulation from Indian plate collision in the Tibetan Plateau appears to be the main reason for the increase in the residual gravity field in that region.
Resolving co- and early post-seismic slip variations of the 2021 MW 7.4 Madoi earthquake in east Bayan Har block with a block-wide distributed deformation mode from satellite synthetic aperture radar data
Shuai Wang, Chuang Song, ShanShan Li, Xing Li
2022, 6(1): 108 -122. doi: 10.26464/epp2022007
On 21 May 2021 (UTC), an MW 7.4 earthquake jolted the east Bayan Har block in the Tibetan Plateau. The earthquake received widespread attention as it is the largest event in the Tibetan Plateau and its surroundings since the 2008 Wenchuan earthquake, and especially in proximity to the seismic gaps on the east Kunlun fault. Here we use satellite interferometric synthetic aperture radar data and subpixel offset observations along the range directions to characterize the coseismic deformation of the earthquake. Range offset displacements depict clear surface ruptures with a total length of ~170 km involving two possible activated fault segments in the earthquake. Coseismic modeling results indicate that the earthquake was dominated by left-lateral strike-slip motions of up to 7 m within the top 12 km of the crust. The well-resolved slip variations are characterized by five major slip patches along strike and 64% of shallow slip deficit, suggesting a young seismogenic structure. Spatial–temporal changes of the postseismic deformation are mapped from early 6-day and 24-day InSAR observations, and are well explained by time-dependent afterslip models. Analysis of Global Navigation Satellite System (GNSS) velocity profiles and strain rates suggests that the eastward extrusion of plateau is diffusely distributed across the east Bayan Har block, but exhibits significant lateral heterogeneities, as evidenced by magnetotelluric observations. The block-wide distributed deformation of the east Bayan Har block along with the significant co- and post-seismic stress loadings from the Madoi earthquake imply high seismic risks along regional faults, especially the Tuosuo Lake and Maqên–Maqu segments of the Kunlun fault that are known as seismic gaps.
Cretaceous–Cenozoic regional stress field evolution from borehole imaging in the southern Jinzhou area, western Liaoning, North China Craton
ChengWei Yang, ChengHu Wang, GuiYun Gao, Pu Wang
2022, 6(1): 123 -134. doi: 10.26464/epp2022001
The Mesozoic Yanshanian Movement affected the tectonic evolution of the North China Craton (NCC). It is proposed that Mesozoic cratonic destruction peaked ~125 Ma, possibly influenced by subduction of the western Pacific Plate beneath the Euro-Asian Plate in the Early Cretaceous. The southern Jinzhou area in the eastern block of the NCC preserves clues about the tectonic events and related geological resources. Studies of the regional stress field evolution from the Cretaceous to the Cenozoic can enhance our understanding of the tectonics and dynamics of the NCC. Borehole image logging technology was used to identify and collect attitudes of tensile fractures from 11 boreholes; these were subdivided into four groups according to dip direction, i.e., NNW-SSE, NWW-SEE, W-E and NE-SW. The development of these fractures was controlled primarily by the regional tectonic stress field; temperature, lithology, and depth contributed to some extent. In 136–125 Ma in the Early Cretaceous, the area was characterized by extension that was oriented NNW-SSE and NWW-SEE; from 125–101 Ma the extension was oriented W-E; after 101 Ma it was NE-SW. This counterclockwise trend has persisted to the present, probably related to oblique subduction of the Pacific Plate, and is characterized by ongoing extension that is nearly N-S-oriented and NEE-SWW-oriented compression.
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