Towards fast focal mechanism inversion of shallow crustal earthquakes in the Chinese mainland

We have developed an automatic regional focal mechanism inversion system based on the Earthquake Rapid Report(ERR) system and the real-time three-component seismic waveform stream of 1 000 broadband seismic stations provided by the China Earthquake Networks Center(CENC). The system can rapidly provide a double couple solution and centroid depth within 5–15 min after receiving earthquake information from the ERR system.The data processing is triggered by earthquake information obtained from the ERR system. The system is capable of determining the focal mechanism of all shallow-depth earthquakes in the Chinese mainland with a magnitude of 5.5–6.5. It utilizes waveform data recorded by seismic stations located within 500 km from the epicenter,enabling the reporting of a focal mechanism solution within 5–15 min of an earthquake occurrence. Additionally,the system can assign a corresponding grade(A B C) to the focal mechanism solution. We processed a total of 301earthquakes that occurred from 2021 to June 2022, and after the quality control, 166 of them were selected.These selected solutions were manually checked, and 160 of them were compiled in a focal mechanism catalog.This catalog can be conveniently downloaded online via the Internet. The automatic focal mechanism solution of earthquakes in eastern China exhibits a good agreement with that provided by the Global Centroid Moment Tensor(GCMT), when available. The average Kagan angle between this catalog and GCMT is 22°, and the average difference in MWis 0.17. Furthermore, compared with GCMT, the minimum magnitude of our catalog has been reduced from approximately 5.0 to 4.0. The correlation between the centroid depth and crustal thickness in the Chinese mainland confirms the distribution of the centroid depth.

Spatial distribution and focal mechanism solutions of the Wenchuan earthquake series:Results and implications

We relocate the spatial distribution of its aftershocks. The relocation database is obtained the devastating 12 May 2008 Wenchuan earthquake and from 89 stations deployed by the China Earthquake Administration, including 54 525 seismograms from 1 376 local earthquakes over Ms3.5 between 12 May 2008 and 3 August 2008. The cross-correlation technique used in this paper has greatly improved the relocation precision by giving much more accurate P-wave differential travel-time measurements than those obtained from routinely picked phase onsets. At the same time, we pick P-wave polarity observations of the Wenchuan earthquake series （hereafter referred to as WES） from 1023 stations in China and 59 IRIS （Incorporated Research Institutions of Seismology） stations. Then, employing a newly developed program CHNYTX, we obtain 83 well-determined focal mechanism solutions （hereafter referred to as FMSs）. Based on spatial distribution and FMSs of the WES, we draw following conclusions： （1） The region near the main shock exhibits a buried low-angle northwest-dipping seismic zone with the main shock at its upper end and two conjugated seismic zones dipping southeast with roughly equal dip-angle; （2） The compressional directions of all kinds of FMSs of the WES are subhorizontal, which reflects the dominant stress in this area is eompressional; （3） The principal compressional direction of the regional stress around Wenchuan is roughly perpendicular to the strike of Beichuan-Yingxiu fault, while around Qingchuan it is roughly parallel to the strike of Qingehuan fault. In intermediate part of the Longmenshan area, the principal compressional direction of the stress should be in-between; （4） The possibly existed molten materials in the lower crust of Songpan-Garze terrain have small contribution to the local stress state in Longmenshan area. The listric geometries of the Longmenshan faults most probably resulted from subhorizontal compression along NW-SE direction in history.

Focal Mechanism Solutions of the 2008 Wenchuan earthquake sequence from P-wave polarities and SH/P amplitude ratios:new results and implications

Abstract The 2008 Wenchuan earthquake, a major intraplate earthquake with Mw 7.9, occurred on the slowly deforming Longmenshan fault. To better understand the causes of this devastating earthquake, we need knowledge of the regional stress field and the underlying geodynamic processes. Here, we determine focal mechanism solutions （FMSs） of the 2008 Wenchuan earthquake sequence （WES） using both P-wave first-motion polarity data and SH/P amplitude ratio （AR） data. As P-wave polarities are more reliable information, they are given priority over SH/ PAR, the latter of which are used only when the former has loose constraint on the FMSs. We collect data from three categories： （1） permanent stations deployed by the China Earthquake Administration （CEA）; （2） the Western Sichuan Passive Seismic Array （WSPSA） deployed by Institute of Geology, CEA; （3） global stations from Incorporated Research Institutions for Seismology. Finally, 129 events with magnitude over Ms 4.0 in the 2008 WES are identified to have well-constrained FMSs. Among them, 83 are well constrained by P-wave polarities only as shown by Cai et al. （Earthq Sci 24（1）：115-125,2011）, and the rest of which are newly constrained by incorporating SH/P AR. Based on the spatial distribution and FMSs of the WES, we draw following conclusions： （1） the principle compressional directions of most FMSs of the WES are subhorizontal, generally in agreement with the conclusion given by Cai et al. （2011） but with a few modifications that the compressional directions are WNW-ESE around Wenchuan and ENE-WSW around Qingchuan, respectively. The subhorizontal compressional direction along the Longmenshan fault from SW to NE seems to have a leftlateral rotation, which agrees well with regional stress field inverted by former researchers （e.g., Xu et al., Acta Seismol Sin 30（5）, 1987; Acta Geophys Sin 32（6）, 1989; Cui et al., Seismol Geol 27（2）：234-242, 2005）; （2） the FMSs of the events not only reflected the regional stress state of the Longmenshan region, but also were obviously controlled by the faults to some extent, which was pointed out by Cai et al. （2011） and Yi et al. （Chin J Geophys 55（4）：1213-1227, 2012）; （3） while the 2008 Wenchuan earthquake and some of its strong aftershocks released most of the elastic energy accumulated on the Longmen- shan fault, some other aftershocks seem to occur just for releasing the elastic energy promptly created by the 2008 Wenchuan earthquake and some of its strong aftershocks. （4） Our results further suggest that the Longmenshan fault from Wenchuan to Beichuan was nearly fully destroyed by the 2008 Wenchuan earthquake and accordingly propose that there is less probability for great earthquakes in the middle part of the Longmenshan fault in the near future, although there might be a barrier to the southwest of Wenchuan and it is needed to pay some attention on it in the near future.

Preliminary estimation for the focal mechanisms of 1996 Lijiang main shock in Yunnan Province and studies of related problems

The mechanisms of the February 3, 1996 Lijiang main shock, Yunnan Province, are estimated by using the principle to inverse the mechanisms of two point sources simultaneously. The results are that the main shock of Lijiang consists of two large ruptures, the time difference and the distance between the two ruptures are about 12 s (by the inversion) and about 26 km respectively. An extensional normal with strike-slip fault in about the north-south direction was formed by the first rupture, the mechanism of the second rupture is to be further studied. The method to inverse mechanisms of two point sources at the same time and the results obtained by directly analyzing P waveform records of the main shock are introduced, some related problems are also discussed. The Wuding earthquakes of October, 1995 and the Lijiang earthquake are considered to be the manifestation of the same dynamic process at different temporal and spatial points and the occurrence order of the two earthquakes is related to the direction of dynamics transmission.

Mssbauer Spectroscopic Studies on a Supersaturated Solid Solution of Fe-Cu Formed by Mechanical Alloying

Mechanical alloying (MA) was employed to produce supersaturated solid solutions of Fe1-xCux,which is virtually immiscible under an equilibrium condition at ambjent temperature. The X-ray diffraction results show that the solutions formed in the concentration ranges of x≤0.1 5 and x≥0.40 are of bcc structure of iron and fcc structure of copper. respectively. For the region in between.however, the alloy obtained is a mixture of bcc plus fcc phases. The Mossbauer spectrum of the solid solution of a single phase could be fitted by two sub-spectra with hyperfine magnetic fields of 200 and 250 kOe. respectively. suggesting that there must exist two forms of coordination in the solution. While to fit the spectrum for the solution with mixed structu re. three Sub-spectra. including a spectrum of α-Fe, should be used. The variation of the Mossbauer spectra of Fe60Cu40 with milling time as well as annealing temperature was systematically studied. This may be ascribed to the changes of the number of nearest neighboring atoms of iron in the processes of formation and decomposition of the solid solution during milling and annealing

Fault plane solutions in Sichuan-Yunnan rhombic block and their dynamic implica-tions

Harvard Centroid Moment Tensor （CMT） solutions for earthquakes from 1977 to 2004 showed that the stress fields are obviously different in northwestern Sichuan sub-block （NWSSB）, western parts of Central Yunnan sub-block （CYSB） and eastern part of CYSB. The characteristics of the mean stress fields in these three regions are obtained by fitting to CMT solutions. The stress state in NWSSB is characterized by its sub-horizontal tensile principal axis of stress （T axis） in roughly N-S direction and west dipping compressive principal axis of stress （P axis）; the one in western part of CYSB is characterized by its ENE dipping T axis and sub-horizontal medium principal axis of stress （B axis） in roughly N-S direction; the one in eastern part of CYSB is characterized by its sub-horizontal P axis in roughly NNW-SSE direction and sub-horizontal T axis in roughly WSW-ENE direction. Finite element method simulation clearly shows that the Indian Plate imposes great extrusion on Sichuan-Yunnan rhombic block （SYRB） near Assam massif. The value of the simulated compressive principal stress decreases with the distance from Assam massif. The simulated directions of the T axes in SYRB form annular distribution encir cling Assam. For a homogeneous elastic medium with free boundary conditions on the top and bottom surfaces as well as the displacement boundary conditions derived from the GPS observations on the lateral boundaries, the computation results are consistent with the Harvard CMT solutions in NWSSB and western part of CYSB, while inconsistent with the Harvard CMT solutions in eastern part of CYSB. The inconsistency in eastern part of CYSB can be reduced when it includes inhomogeneous elastic media. The stress states in NWSSB and western part of CYSB revealed by the Harvard CMT solutions are not local, which are mainly controlled by the boundary force on the whole region. On the other hand, the stress state in eastern part of CYSB given by the Harvard CMT solutions is local, which may be affected by local topography, material inhomogeneity, and the drag force underneath.

Study on three independent parameters of focal mechanism solution

In this paper, the relationships of the plunges and azimuths of T and P axes versus the strikes, dips, and rakes of two seismic nodal planes were derived to provide ref- erence for earthquake researchers. The independence of the plunges and azimuths of T, B, and P axes in focal mech- anism solution was discussed, and it was concluded that three parameters, i.e., the azimuths of T, B and P axes, are completely independent. The focal mechanism solution representation based on Euler rotation was introduced, using three Euler angles in place of the plunges and azi- muths of T, B, and P axes, and three focal mechanism solution representations were briefly compared and ana- lyzed in respect of accuracy on the basis of the assumption of rounding; it was concluded that the Euler angle repre- sentation has better accuracy, compared with the azimuth representation and the traditional representation with T, B, and P axes.

Types of focal mechanism solutions and parameter consistency of the sub-blocks in Sichuan and Yunnan Provinces

Based on P- and S-wave amplitudes and some clear initial P-wave motion data, we calculated focal mechanism solutions of 928 M≥2.5 earthquakes （1994-2005） in four sub-blocks of Sichuan and Yunnan Provinces, namely Sichuan-Qinghai, Yajiang, Central Sichuan and Central Yunnan blocks. Combining these calculation results with those of the focal mechanism solutions of moderately strong earthquakes, we analyzed the stress field characteristics and dislocation types of seismogenic faults that are distributed in the four sub-blocks. The orientation of principal compressive stress for each block is： EW in Sichuan-Qinghai, ESE or SE in Yajiang, Central Sichuan and Central Yunnan blocks. Based on a great deal of focal mechanism data, we designed a program and calculated the directions of the principal stress tensors, σ1, σ2 and σ3, for the four blocks. Meanwhile, we estimated the difference （also referred to as consistency parameter θ^- ） between the force axis direction of focal mechanism solution and the direction of the mean stress tensor of each block. Then we further analyzed the variation of θ^- versus time and the dislocation types of seismogenic faults. Through determination of focal mechanism solutions for each block, we present information on the variation in θ^- value and dislocation types of seismogenic faults.

Role of Microstructure and Spectrum Features on the Catalysis Effect of Ce1-x(Nd0.5Eu0.5)xO2-δSolid Solutions

Nanosized Ce^1-x）（Nd^0.5）Eu^0.5））xO^2-δ） solid solutions（x = 0.00-0.20） were synthesized by means of hydrothermal method.Then the solid solutions were ball milled with Mg2Ni and Ni powders for 20 h to get the Mg2Ni–Ni–5 mol% Ce^1-x）（Nd^0.5）Eu^0.5））xO^2-δ） composites.The structures and spectrum characteristics of the Ce^1-x）（Nd^0.5）Eu^0.5））xO^2-δ） solid solutions catalysts were analyzed systemically.XRD results showed that the doped samples exhibited single phase of CeO2 fluorite structure.The cell parameters and cell volumes were increased with increasing the doped content.Raman spectrum revealed that the peak position of F^2g mode shift to higher wavenumbers and the peak corresponding to oxygen vacancies were observed distinctly for the doped samples.UV-Vis technique indicated that the absorption peaks of Eu^3＋ and Nd^3＋ ions appeared; the bandgap energy was decreased linearly.The electrochemical and kinetic properties of the Mg2Ni–Ni–5 mol% Ce1-x（Nd0.5Eu0.5xO2-δ composites were measured.The maximum discharge capacity was increased from 722.3 mA h/g for x = 0.00 to 819.7 mA h/g for x = 0.16,and the cycle stability S20 increased from 25.0%（x = 0.00） to 42.2%（x = 0.20）.The kinetic measurement proved that the catalytic activity of composite surfaces and the hydrogen diffusion rate were improved for the composites with doped catalysts,especially for the composites with x = 0.16 and x = 0.20.The catalysis mechanism was analyzed from the point of microstructure and spectrum features of the Ce1-x（Nd0.5Eu0.5）xO2-δ solid solutions.

Influence and Suggestions on Trial Implementation Measures for Early Settlement Mechanism of Drug Patent Disputes

Objective To study the core contents of the“Implementation Measures for Early Settlement Mechanism of Drug Patent Disputes(Trial)”in China,and to clarify the concerns for enterprises in future work.Methods A comprehensive review of the literature was used to find out the key regulations for detailed decomposition and analysis.Results and Conclusion By analyzing the key clauses of China’s“Implementation Measures for Early Settlement Mechanism of Drug Patent Disputes(Trial)”,some practical countermeasures and suggestions are put forward for related research and development(R&D)innovation and drug declaration of enterprises.

Crustal stress field in Yunnan: implication for crust-mantle coupling

We applied the g CAP algorithm to determine 239 focal mechanism solutions 3：0≤MW≤ 6：0） with records of dense Chin Array stations deployed in Yunnan,and then inverted 686 focal mechanisms（including 447 previous results） for the regional crustal stress field with a damped linear inversion. The results indicate dominantly strike-slip environment in Yunnan as both the maximum（r1） and minimum（r3） principal stress axes are sub-horizontal. We further calculated the horizontal stress orientations（i.e., maximum and minimum horizontal compressive stress axes： S H and S h, respectively） accordingly and found an abrupt change near ＊26°N. To the north, S H aligns NW-SE to nearly E-W while S h aligns nearly N-S. In contrast, to the south, both S H and S h rotate laterally and show dominantly fan-shaped patterns. The minimum horizontal stress（i.e., maximum strain axis） S h rotates from NW-SE to the west of Tengchong volcano gradually to nearly E-W in west Yunnan, and further toNE-SW in the South China block in the east. The crustal strain field is consistent with the upper mantle strain field indicated by shear-wave splitting observations in Yunnan but not in other regions. Therefore, the crust and upper mantle in Yunnan are coupled and suffering vertically coherent pure-shear deformation in the lithosphere.

Normal Faulting Type Earthquake Activities in the Tibetan Plateau and Its Tectonic Implication

This paper analyzes various earthquake fault types, mechanism solutions, stress field as well as other geophysical data to study the crust movement in the Tibetan plateau and its tectonic implications. The results show that a lot of normal faulting type earthquakes concentrate in the central Tibetan plateau. Many of them are nearly perfect normal fault events. The strikes of the fault planes of the normal faulting earthquakes are almost in the N-S direction based on the analyses of the equal area projection diagrams of fault plane solutions. It implies that the dislocation slip vectors of the normal faulting type events have quite great components in the E-W direction. The extension is probably an eastward extensional motion, mainly a tectonic active regime in the altitudes of the plateau. The tensional stress in the E-W or WNW-ESE direction predominates the earthquake occurrence in the normal event region of the central plateau. A number of thrust fault and strike-slip fault type earthquakes with strong compressive stress nearly in the NNE-SSW direction occurred on the edges of the plateau. The eastward extensional motion in the Tibetan plateau is attributable to the eastward movement of materials in the upper mantle based on_seismo-tomographic results. The eastward extensional motion in the Tibetan plateau may be related to the eastward extrusion of hotter mantle materials beneath the east boundary of the plateau. The northward motion of the Tibetan plateau shortened in the N-S direction probably encounters strong obstructions at the western and northern margins. Extensional motions from the relaxation of the topography and/or gravitational collapse in the altitudes of the plateau occur hardly in the N-S direction. The obstruction for the plateau to move eastward is rather weak.

Spatio-temporal variation of the stress field in the Wenchuan aftershock region

Focal mechanism solutions and centroid depths of 312 M≥4 aftershocks from the 2008 Wenchuan earthquake sequence have been derived by CAP （Cut and Paste） method from broadband waveform data with relatively high signal-to-noise ratio （SNR）. Following this, we have analyzed the distribution of focal depths and the stress tensors, as well as the types of focal mechanisms. The major results are： （1） different cross-sections show that the depth ranges of the aftershocks at the southern and northern ends of the aftershock area along the Longmenshan fault zone are wider than those on the central segment, where rare M≥4 aftershocks occurred at depths shallower than 10 kin. The main faults trend to the NW on the southern and central segments, and for the northern segment, no dominant trend direction has been determined; （2） stress tensor distribution demonstrates that the majority of the aftershock areas on the cross-section along the major axis are mainly under compressive stress perpendicular to the profile; however, for the areas near Lixian, Beichuan, Qingchuan and the shallow parts of its northern segment, large principal stress components are parallel to the major axis profile direction. On the cross-sections perpendicular to the major axis, the three areas above can be divided into two parts： one with dominantly compressional stress near the major faults of the Longmenshan fault zone on the SE side, and the other with NE-direction push along the fault zone on the NW side; （3） the stress tensor distribution in map view is very similar to those on the vertical cross-sections. In map view, the orientation of the principal compressional stress axis $1 on the central segment of the aftershock area presents an SE-trending arc shape; （4） the stress tensor slices at different depths show that the orientation of S1 axis mainly changes on the central segment and at the northern end, indicating that the two segments have different seismogenic structures at different depths; （5） with the exception of the northern end of the aftershock region, the orientation of the $1 axis changes little during the early and late stages, illustrating the seismogenic structures are relatively stable; （6） preliminary analyses for the seismogenic structures at the northern end indicated that deeper strike-slip quakes occurred on the ENE-striking branch at first, and then the NNE-striking branch faults at the northern end were activated and generated a series of relatively shallow strike-slip earthquakes due to subsequent stress-triggering; （7） the aftershock triggering mechanism that occurred near Lixian is different between the shallow and deep depths, and between the early and late stages, indicating that the main faults and the branch faults responsible for aftershocks are at different depths. Consequently, the relaxation effect of the main shock particularIy impacts the branch faults.

The seismicity and tectonic stress field characteristics of the Longmenshan fault zone before the Wenchuan M_S8.0 earthquake

The seismicity of Longrnenshan fault zone and its vicinities before the 12 May 2008 Wenchuan Ms8.0 earthquake is studied. Based on the digital seismic waveform data observed from regional seismic networks and mobile stations, the focal mechanism solutions are determined. Our analysis results show that the seismicities of Longmenshan fault zone before the 12 May 2008 Wenchuan earthquake were in stable state. No obvious phenomena of seismic activity intensifying appeared. According to focal mechanism solutions of some small earthquakes before the 12 May 2008 Wenchuan earthquake, the direction of principal compressive stress P-axis is WNW-ESE. The two hypocenter fault planes are NE-striking and NW-striking. The plane of NE direction is among N50°-70°E, the dip angles of fault planes are 60°-70° and it is very steep. The faultings of most earthquakes are dominantly characterized by dip-slip reverse and small part of faultings present strike-slip. The azimuths of principal compressive stress, the strikes of source fault planes and the dislocation types calculated from some small earthquakes before the 12 May 2008 Wenchuan earthquake are in accordance with that of the main shock. The average stress field of micro-rupture along the Longmenshan fault zone before the great earthquake is also consistent with that calculated from main shock. Zipingpu dam is located in the east side 20 km from the initial rupture area of the 12 May 2008 Wenchuan earthquake. The activity increment of small earthquakes in the Zipingpu dam is in the period of water discharging. The source parameter results of the small earthquakes which occurred near the initial rupture area of the 12 May 2008 Wenchuan earthquake indicate that the focal depths are 5 to 14 km and the source parameters are identical with that of earthquake.

Fine relocation, mechanism, and tectonic indications of middle-small earthquakes in the Central Tibetan Plateau

The medium-small earthquakes that occurred in the middle part of Tibetan Plateau(32°N–36°N, 90°E–93°E) from August 2016 to June 2017 were relocated using the absolute earthquake location method Hypo2000. Compared to the reports of Chinese Seismological Networks, our relocation results are more clustered on the whole, the horizontal location differences exceed 10 km, and the focal depths are concentrated in 0–8 km, which indicates that the upper crust inside the Tibetan Plateau is tectonically active. In June2017 altogether eight earthquakes above magnitude 3.0 took place; their relocated epicenters are concentrated around Gêladaindong.The relocation results of M<3.0 small earthquakes also showed obvious differences. Therefore, we used the CAP method to invert for the focal mechanisms of the M ≥3.0 earthquakes; results generally tally with the surface geological structures, indicating that the Tibetan Plateau is still under the strong compressional force from the India Plate. Among them the eight earthquakes that occurred near Gêladaindong in June 2017 are all of normal fault type or with some strike-slip at the same time; based on previous research results we conjecture that these events are intense shallow crust responses to deep crust-mantle activities.

Modern tectonic stress field in Southwest Yunnan, China

By means of inversion of fault slip data, the parameters of 20 tectonic stress tensors in Southwest Yunnan region are determined. Compared with the average stress field of the region obtained from focal mechanism solutions, the following characteristics of modern tectonic stress field in this region are obtained. From the west of Zhenyuan-Yingpanshan fault to the south of Longling fault zone, the maximum compressional stress is in NNE direction and the stress regime is mainly of strike-slip type. In Longling fault zone and the area north to it, the direction of maximum compressional stress is near-NS or NNW, the stress regime is of strike-slip type.

Spatio-temporal variation and focal mechanism of the Wenchuan M_S8.0 earthquake sequence

Based on abundant aftershock sequence data of the Wenchuan Ms8.0 earthquake on May 12, 2008, we studied the spatio-temporal variation process and segmentation rupture characteristic. Dense aftershocks distribute along Longmenshan central fault zone of NE direction and form a narrow strip with the length of 325 krn and the depth between several and 40 km. The depth profile （section of NW direction） vertical to the strike of aftershock zone （NE direction） shows anisomerous wedgy distribution characteristic of afiershock concentrated regions; it is related to the force form of the Longmenshan nappe tectonic belt. The stronger aftershocks could be divided into northern segment and southern segment apparently and the focal depths of strong aftershocks in the 50 km area between northern segment and southern segment are shallower. It seems like ＇to be going to rupture＇ segment. We also study focal mechanisms and segmentation of strong aftershocks. The principal compressive stress azimuth of aftershock area is WNW direction and the faulting types of aftershocks at southern and northern segment have the same proportion. Because afiershocks distribute on different secondary faults, their focal mechanisms present complex local tectonic stress field. The faulting of seven strong earthquakes on the Longmenshan central fault is mainly characterized by thrust with the component of right-lateral strike-slip. Meantime six strong aftershocks on the Longmenshan back-range fault and Qingchuan fault present strike-slip faulting. At last we discuss the complex segmentation rupture mechanism of the Wenchuan earthquake.

A multiscale 3D finite element analysis of fluid/solute transport in mechanically loaded bone

The transport of fluid, nutrients, and signaling molecules in the bone lacunar-canalicular system （LCS） is critical for osteocyte survival and function. We have applied the fluorescence recovery after photobleaching （FRAP） approach to quantify load-induced fluid and solute transport in the LCS in situ, but the measurements were limited to cortical regions 30-50 μm underneath the periosteum due to the constrains of laser penetration. With this work, we aimed to expand our understanding of load-induced fluid and solute transport in both trabecular and cortical bone using a multiscaled image-based finite element analysis （FEA） approach. An intact murine tibia was first re-constructed from microCT images into a three-dimensional （3D） linear elastic FEA model, and the matrix deformations at various locations were calculated under axial loading. A segment of the above 3D model was then imported to the biphasic poroelasticity analysis platform （FEBio） to predict load-induced fluid pressure fields, and interstitial solute/fluid flows through LCS in both cortical and trabecular regions. Further, secondary flow effects such as the shear stress and/or drag force acting on osteocytes, the presumed mechano-sensors in bone, were derived using the previously developed ultrastructural model of Brinkman flow in the canaliculi. The material properties assumed in the FEA models were validated against previously obtained strain and FRAP transport data measured on the cortical cortex. Our results demonstrated the feasibility of this computational approach in estimating the fluid flux in the LCS and the cellular stimulation forces （shear and drag forces） for osteocytes in any cortical and trabecular bone locations, allowing further studies of how the activation of osteocytes correlates with in vivo functional bone formation. The study provides a promising platform to reveal potential cellular mechanisms underlying the anabolic power of exercises and physical activities in treating patients with skeletal deficiencies.

Preliminary analysis on the tectonic stress level in the source region of Tangshan earthquake

The abundant data of focal mechanism solutions in Tangshan region, China, are inverted for the tectonic stress field. Combined with tectonophysical consideration, the magnitude of the three principal stresses, as well as their vertical variation under the average crustal rock property, in the source region of the 1976 Tangshan earthquake is estimated. The relationship between crustal stress and friction mc, pore pressure P0 and stress shape factor F is studied. The paper draws the conclusion that the vertical increasing rate of the maximum principal stress s is directly proportional to friction, and inversely to pore pressure P0 and stress shape factor F ; while the vertical increasing rate of the minimum principal tress s is directly proportional to pore pressure P0, inversely to friction mc and stress shape factor F. This study is a try to invert the data of focal mechanism solutions for the complete stress tensor.

Temporal evolution of the focal mechanism consistency of the 2021 Yangbi M_(S) 6.4 earthquake sequence in Yunnan

Using the Cut And Paste(CAP)method,we invert the focal mechanism of 38 moderate earthquakes(M_(S)≥3.0)recorded by Yunnan seismic network and analyze the corresponding focal mechanism consistency based on the minimum spatial rotation angle.Our results indicate that the M_(S)6.4 mainshock is induced by a lateral strike slip fault(with a rake angle of~-165°)and a little normal-faulting component event along a nearly vertical plane(dipping angle~79° and strike~138°).Combining our results with high resolution catalog,we argue that the seismogenic fault of this earthquake sequence is a secondary fault western to the major Weixi-Qiaohou-Weishan fault.The focal mechanism evolution can be divided into three periods.During the first period,the foreshock sequence,the focal mechanism consistency is the highest(KA<36°);during the second period which is shortly after the mainshock,the focal mechanism shows strong variation with KA ranging from 8° to 110°;during the third period,the seismicity becomes weak and the focal mechanism of the earthquakes becomes more consistent than the second period(18°<KA<73°).We suggest that the KA,to some extent,represents the coherence between local tectonic stress regime and the stress state of each individual earthquake.Furthermore,high focal mechanism consistency and high linearity of seismic distribution may serve as indicators for the identification of foreshock sequence.