East-west Direction Research Articles

Climate Change Impacts on the Potential Distribution and Range Shift of Dendroctonus ponderosae (Coleoptera: Scolytidae)

Dendroctonus ponderosae Hopkins (Coleoptera: Scolytidae) is one of the most important bark beetles in North America and causes considerable economic and ecological losses during outbreaks. The distribution of this pest species is likely to be altered by climate change, which may threaten currently unaffected areas. In this study, we used CLIMEX to project the potential global distribution of D. ponderosae according to both historical climate data (1987–2016) and future climate warming estimates (2021–2100) to evaluate the impact of climate change on this species. Regions with suitable climate for D. ponderosae are distributed in all continents except Antarctica under both historical and future climate conditions, and these are predicted to change continuously with climate change. Overall, climate suitability will increase in middle- and high-latitude regions and decrease in low-latitude regions, and regions most sensitive to climate change are located in the mid-latitude zone. Moreover, the shift directions and ranges of climate-suitable regions under future conditions will differ among continents, and the shift distances in the north–south direction are larger than these in the east–west direction for Africa, Asia, Europe, South America, and Oceania, indicating that shift direction is possibly mainly affected by temperature. These projected distributions may provide theoretical guidance for early-warning intervention and risk assessment.

The ALMA Discovery of the Rotating Disk and Fast Outflow of Cold Molecular Gas in NGC 1275

Abstract We present observations using the Atacama Large Millimeter/submillimeter Array of the CO(2−1), HCN(3−2), and HCO+(3−2) lines in the nearby radio galaxy/brightest cluster galaxy (BCG) NGC 1275 with a spatial resolution of ∼20 pc. In previous observations, the CO(2−1) emission was detected as radial filaments lying in the east–west direction on a kiloparsec scale. We resolved the inner filament and found that it cannot be represented by a simple infalling stream on a sub-kiloparsec scale. The observed complex nature of the filament resembles the cold gas structure predicted by numerical simulations of cold chaotic accretion. Within the central 100 pc, we detected a rotational disk of molecular gas whose mass is ∼108 M ⊙. This is the first evidence of the presence of a massive cold gas disk on this spatial scale for BCGs. A crude estimate suggests that the accretion rate of the cold gas can be higher than that of hot gas. The disk rotation axis is approximately consistent with the radio-jet axis. This probably suggests that the cold gas disk is physically connected to the innermost accretion disk, which is responsible for jet launching. We also detected absorption features in the HCN(3−2) and HCO+(3−2) spectra against the radio continuum emission mostly radiated by a jet of size ∼1.2 pc. The absorption features are blueshifted from the systemic velocity by ∼300–600 km s−1, suggesting the presence of outflowing gas from the active galactic nucleus (AGN). We discuss the relation of the AGN feeding with cold accretion, the origin of blueshifted absorption, and an estimate of the black hole mass using molecular gas dynamics.

Positioning buildings on a zoning island to provide maximum shading: a case study

Because summer days are long, and the weather is too hot, people desire shady spaces to escape the overwhelming effect of the sun. To keep buildings and open-air environments in the shade, a suitable building location design may be created at the planning stage. Positioning of buildings and recreation areas in the maximum amount of shade is closely dependent on the location of the buildings to be built, the distance between the buildings, the time of the day and the sun angles at a particular hour. It was found necessary to carry out this study, since no study was found to be carried out regarding the positioning of buildings in the maximum amount of shade. For buildings to be built in residential areas, separate or block arrangements are applied. This study discusses a building to be built on a reconstruction island in Adana in the Eastern Mediterranean Region of Turkey. First of all, the shading effects of the buildings adjacent to the building in a parcel were examined in detail based on various positions of the façades of the building and different values of the solar azimuth. As a result of the study, the positioning of the buildings for providing the maximum shading was investigated. If the front and rear façades of the buildings were located in the west-east direction, according to the positioning of the buildings in the north-south direction, the front and rear façades would be exposed to less sunlight and more shade. In h = ± 6 sun hours, the façades of buildings in the parcels facing the north were under the influence of the sun rays coming from the side, and the rear façades of the buildings were in the shade.

Fracture systems and petrophysical properties of tight sandstone undergoing regional folding: A case study of the Cretaceous reservoirs in the Kuqa foreland thrust belt, Tarim Basin

Abstract The Kuqa foreland thrust belt of the Tarim Basin hosts a prolific hydrocarbon system. The main reservoirs are characterized by tight sandstone with low-porosity and ultra-low permeability, buried presently at more than 5000 m depth. Natural fracture systems have a significant impact on reservoir performance, and it may form paths for fluid flow in tight sandstone reservoirs, and therefore plays an essential role in controlling high production rates. With the aim of analyzing the distribution of favorable reservoir, we studied subsurface fracture patterns and petrophysical properties of the Bashijiqike Formation with data collected from Dabei structure and Keshen structure. We document the presence of four fracture systems whose distribution is related to far-field stress, thrusting and folding. In the Keshen anticlines, higher fracture intensities are observed in the limbs, with principal east-west (hinge-parallel fracture system) direction. The hinge-parallel fracture system includes a moderate-dipping fracture set and a vertical fracture set. Crosscutting relationships stress field inversion and fracture surface textures suggest that the moderate-dipping fracture set consists of shear fractures and can be explained by intra-layer shear caused by thrusting. The vertical fracture set may be formed due to the local outer arc extension during folding. The oblique fracture system shows scattering in strike, and is supposed to be related to a shear event of locally left-lateral strike-slip. Whereas, in the Dabei anticlines, the major system is hinge-perpendicular fracture system (NW-SE), showing a trending of increasing fracture intensity from limbs to hinge. The hinge-perpendicular fractures system in the Dabei anticlines consist of shear fractures and tension fractures. Stress inversion result shows it corresponds to northwest-southeast orientation compression stage. Besides, we analyzed petrophysical properties include porosity, permeability, Young's module, Poisson ratio and compressive strength of the Bashijiqike Formation concerning their structural position within folds. It indicates that the highest porosity and permeability are associated with dissolution and fracturing. The compressive strength of different structural positions also restrict the variations of mechanical properties of rocks. The best reservoir quality is suggested in the hinge zone and areas close to thrust. The findings have given maybe helpful for providing favorable reservoir targets for prospecting in the compressional basin.

The discovery of secondary lobes in the Seyfert galaxy NGC 2639

ABSTRACT We report the discovery of a secondary pair of radio lobes in the Seyfert galaxy NGC 2639 with polarization-sensitive observations with the Karl G. Jansky Very Large Array (VLA). The presence of these lobes, which are aligned nearly perpendicular to the known set of radio lobes observed in the east–west direction, has not been reported previously in the literature. The in-band rotation measure image shows gradients in both the lobes indicative of organized magnetic field structures on kpc-scales. The magnetic field structure is aligned with the jet/lobe direction in both the lobes. Based on the settled optical morphology of the host galaxy, it is likely that a minor merger that did not disrupt the host galaxy structure is responsible for the observed features in NGC 2639. This also explains the near 90° change in the jet direction; the current jet direction being the result of a new accretion disc formed by the minor merger, whose direction was a result of the angular momentum of the inflowing merger gas.

Marlim R3D: A realistic model for controlled-source electromagnetic simulations — Phase 2: The controlled-source electromagnetic data set

Synthetic data provided by geoelectric earth models are a powerful tool to evaluate a priori a controlled-source electromagnetic (CSEM) workflow effectiveness. Marlim R3D (MR3D) is an open-source complex and realistic geoelectric model for CSEM simulations of the postsalt turbiditic reservoirs at the Brazilian offshore margin. We have developed a 3D CSEM finite-difference time-domain forward study to generate the full-azimuth CSEM data set for the MR3D earth model. To that end, we fabricated a full-azimuth survey with 45 towlines striking the north–south and east–west directions over a total of 500 receivers evenly spaced at 1 km intervals along the rugged seafloor of the MR3D model. To correctly represent the thin, disconnected, and complex geometries of the studied reservoirs, we have built a finely discretized mesh of [Formula: see text] cells leading to a large mesh with a total of approximately 90 million cells. We computed the six electromagnetic field components (Ex, Ey, Ez, Hx, Hy, and Hz) at six frequencies in the range of 0.125–1.25 Hz. In our efforts to mimic noise in real CSEM data, we summed to the data a multiplicative noise with a 1% standard deviation. Both CSEM data sets (noise free and noise added), with inline and broadside geometries, are distributed for research or commercial use, under the Creative Common License, at the Zenodo platform.

Flooding Along Oda River Due to the Western Japan Heavy Rain in 2018

The heavy rain that hit Western Japan in July 2018 triggered the worst rain-related disaster in the Heisei era, with the total of dead and missing persons exceeding 230, mainly in the Hiroshima and Okayama Prefectures. At several locations along Oda River (of the Takahashi river system) and its tributaries, dikes were breached due to large-scale flood, leaving 51 persons dead. This paper aims to shed light on the scale of inundation along Oda River and its tributaries and identify the characteristics of and critical factors for human damage. Field surveys were conducted to measure flood marks in flooded areas and river channels, and gauge the extent of damage to people and property. The surveys found that a large area was inundated on the north side of Oda River, with an inundation depth exceeding 5 m for 1 km in the south-north direction and 3.5 km in the east-west direction, which made vertical evacuation of residents difficult. The findings that about 80% of the dead were found on the first floor of their houses, with those who had lived in a one-story house and those who had lived in a two-story house accounting for 50% each of the deceased, indicate how difficult even vertical evacuation was. The findings appear to be related to the considerable inundation depth and high rate of water level increase, along with the fact that the majority of the deceased were elderly people.

EFFECTS OF MECHANICALLY STABILIZED GRADED ASSORTED COARSE-GRAINED SOILS IN THE PERFORMANCE OF UNPAVED ROAD: A CASE STUDY IN GOFFA ZONE, SAWLA AREA

Road network development in Ethiopia is booming, radiating from Addis Ababa towards North-South directions, and East-West directions, due to the good economic growth of the country. However, there are challenges always facing by the pavement designers, and materials engineers for every road project, specifically the unpaved roads in Goffa Zone. It was because, most parts of the existing unpaved road sections within the study area are heavily damaged, and lack of proper maintenance. The source of good quality of sub-base course materials limited and becoming depleted. It is for this reason that the research study focused on the investigation of the effects of mechanically stabilized graded assorted coarse-grained soils. Disturbed and undisturbed samples from different quarry sites were considered and tested in the laboratory. Laboratory test for each location performed, and the results served as control values of the engineering properties of natural soils. The Disturbed samples tested for Gradation, Atterberg's Liquid Limit Tests, and Compaction, while, the undisturbed sample tested for the CBR strength, using ASTM manual. The results of the assorted materials for the sub-base course was analyzed and compared with the AASHTO and ERA Standard Specifications.

EFFECTS OF MECHANICALLY STABILIZED GRADED ASSORTED COARSE-GRAINED SOILS IN THE PERFORMANCE OF UNPAVED ROAD: A CASE STUDY IN GOFFA ZONE, SAWLA AREA

Road network development in Ethiopia is booming, radiating from Addis Ababa towards North-South directions, and East-West directions, due to the good economic growth of the country. However, there are challenges always facing by the pavement designers, and materials engineers for every road project, specifically the unpaved roads in Goffa Zone. It was because, most parts of the existing unpaved road sections within the study area are heavily damaged, and lack of proper maintenance. The source of good quality of sub-base course materials limited and becoming depleted. It is for this reason that the research study focused on the investigation of the effects of mechanically stabilized graded assorted coarse-grained soils. Disturbed and undisturbed samples from different quarry sites were considered and tested in the laboratory. Laboratory test for each location performed, and the results served as control values of the engineering properties of natural soils. The Disturbed samples tested for Gradation, Atterberg's Liquid Limit Tests, and Compaction, while, the undisturbed sample tested for the CBR strength, using ASTM manual. The results of the assorted materials for the sub-base course was analyzed and compared with the AASHTO and ERA Standard Specifications.

Photovoltaic systems with vertically mounted bifacial PV modules in combination with green roofs

Dependent on the specific conditions flat roofs can be well suited for the installation of large photovoltaic systems in urban areas. For urban designers also other aspects, such as the insulation of buildings, cooling, air purification and water retention play an important role besides the ecological energy generation. The combination of photovoltaics and roof greening can therefore be an interesting fusion. It combines the advantages of a green roof with the local electrical energy production at the place of consumption.However, using a conventional photovoltaic system with tilted modules in south or east-west direction on a green roof causes problems, as typical low tilt angels and high ground coverage rates result in an almost complete coverage of the roof surface. Plants, growing in between the covered areas provoke undesirable shading of the collector surface. Only a frequent maintenance procedure, complicated by dense PV system layouts, can avoid a reduction of the energy yield in the course of time.Vertically mounted specially designed bifacial modules are an option to realize photovoltaic power generation in combination with a functional green roof at low maintenance costs. In this paper, we report on the layout and the energy yield of a corresponding system. Custom-made bifacial modules with 20 cells were produced and vertically installed in landscape orientation. The narrow layout of the modules lowers the wind load and reduces the visibility. The enhanced power in the morning and evening of vertically east-west installed modules can additionally lead to higher self-consumptions rates.Despite having some shading and undergrounds with albedo factors of less than 0.2, the bifacial installation with a rated power of 9.09 kWp achieved a specific yield of the 942 kWh/kWp in one year (11.08.2017–10.08.2018). This is close to typical values of 1000 kWh/kWp achieved for south-facing PV systems in the same region.The impact of the greening on the albedo and the system performance is investigated in more detail with two smaller sub-systems. The energy yields of the two bifacial sub-systems are compared to a monofacial, south-facing reference module. The use of silver-leaved plants in this system resulted in higher albedo values and a more resilient roof greening.

Characteristics and influence of green tide drift and dissipation in Shandong Rongcheng coastal water based on remote sensing

Green tides in the Yellow Sea have occurred in large-scale blooms since 2007. Originating in the southern Yellow Sea and drifting northward continuously, these green tides have severely affected the coastal ecological environment. To analyze the influence of green tides on marine aquaculture in the Rongcheng coastal water (the northernmost sea area influenced by green tide), we used the Moderate Resolution Imaging Spectrometer (MODIS), GaoFen-1 (GF-1) satellite imagery and the sea surface wind (SSW) data. We also used field investigation to analyze the drift trajectory, drift speed, dissipation speed and distribution density of green tides. The results show that the main body of a green tide will drift northeast and continue in this direction after crossing the Rongcheng Chengshanjiao coastal water. Between 2013 and 2018, the drift speeds of green tides to the north of this area were within 1–5 km/d, the drift speed in the east-west direction was 0.3–4 km/d, and the interannual difference was not significant. The dissipation speed of the green tide in the Rongcheng Sea is generally within the range of 1–5 km2/d and shows little interannual difference. The distribution density in the southern area of Rongcheng is the highest, ranging from 3% to 7%. The area with the highest frequency of influence is also the area with the greatest distribution density of green tides, and disasters are most severe here. A reasonable collection area is proposed, based on the above analysis. This research provides the basis for understanding the characteristics of green tides in the dissipation phase, and the prevention and control methods of green tide disasters in the Rongcheng coastal water.

Average surface flows before the formation of solar active regions and their relationship to the supergranulation pattern.

Context.The emergence of solar active regions is an important but poorly understood aspect of the solar dynamo.Aims.Knowledge of the flows associated with the rise of active-region-forming magnetic concentrations through the near-surface layers will help determine the mechanisms of active region formation.Methods.We used helioseismic holography and granulation tracking to measure the horizontal flows at the surface that precede the emergence of active regions. We then averaged these flows over about sixty emerging active regions to reduce the noise, selecting active regions that emerge into relatively quiet Sun. To help interpret the results, we constructed a simple model flow field by generating synthetic “emergence locations” that are probabilistically related to the locations of supergranulation-scale convergence regions in the quiet Sun.Results.The flow maps obtained from helioseismology and granulation tracking are very similar (correlation coefficients for single maps around 0.96). We find that active region emergence is, on average, preceded by converging horizontal flows of amplitude about 40 ms−1. The convergence region extends over about 40 Mm in the east-west direction and about 20 Mm in the north-south direction and is centered in the retrograde direction relative to the emergence location. This flow pattern is largely reproduced by a model in which active region emergence occurs preferentially in the prograde direction relative to supergranulation inflows.Conclusions.Averaging over many active regions reveals a statistically significant pattern of near-surface flows prior to emergence. The qualitative success of our simple model suggests that rising flux concentrations and supergranule-scale flows interact during the emergence process.

Geoelectrical structure of Ulleung Island, Korea: interpretation of three-dimensional magnetotelluric data

ABSTRACTA three-dimensional (3D) magnetotelluric (MT) survey was carried out to delineate subsurface structures and possible fractures for geothermal development around Ulleung Island, Korea. Good-quality MT data were obtained throughout the survey region with respect to a remote reference located in Sawauchi, Japan, ∼ 900 km from the centre of the field site. 3D modelling and inversion were then performed, considering the sea effect on MT measurements near the coastline. The modelling results showed that seawater surrounding Ulleung Island affected MT data at frequencies below 10 Hz, depending on the distance from the shore. Based on this information, two types of 3D MT data inversion were performed: ordinary 3D inversion and 3D inversion using sea effects as a constraint. 3D inversion using the sea-effect constraint gave more reasonable and reliable results. In addition, the inversion that accounted for sea effects indicated a clear east–west conductive anomaly along the line connecting test boreholes GH-1 and GH-2; a high geothermal gradient of ∼ 100 °C/km was recorded. The geothermal gradients were lower, < 80 °C/km, at boreholes located in the southern (GH-3) and northern (GH-4) regions of the study area. These results suggest that deep circulation of fluid through deeply connected fractures, e.g. the anomaly observed in the east–west direction, carries heat from the bottom depths to near-surface layers. This would explain the large differences in gradients among sites in the study area.

Using the jet stream for sustainable airship and balloon transportation of cargo and hydrogen

The maritime shipping sector is a major contributor to CO2 emissions and this figure is expected to rise in coming decades. With the intent of reducing emissions from this sector, this research proposes the utilization of the jet stream to transport a combination of cargo and hydrogen, using airships or balloons at altitudes of 10–20 km. The jet streams flow in the mid-latitudes predominantly in a west–east direction, reaching an average wind speed of 165 km/h. Using this combination of high wind speeds and reliable direction, hydrogen-filled airships or balloons could carry hydrogen with a lower fuel requirement and shorter travel time compared to conventional shipping. Jet streams at different altitudes in the atmosphere were used to identify the most appropriate circular routes for global airship travel. Round-the-world trips would take 16 days in the Northern Hemisphere and 14 in the Southern Hemisphere. Hydrogen transport via the jet stream, due to its lower energy consumption and shorter cargo delivery time, access to cities far from the coast, could be a competitive alternative to maritime shipping and liquefied hydrogen tankers in the development of a sustainable future hydrogen economy.

CFD Simulation on Leakage and Explosion Accident of Liquefied Hydrocarbon Loading Station and Dynamic Responses Analysis of Control Room

Considering the dangerous characteristics of Liquefied hydrocarbon loading station, a three-dimensional model of a certain liquefied hydrocarbon working area was established to simulate the accident of liquefied hydrocarbon leakage and vapour cloud explosion, and the relationship between the number of loading vehicles and explosion overpressure was analyzed. Meanwhile, the existing control room is not designed for anti-explosion, and the personnel are relatively concentrated, so the dynamic response of the control room under explosion loading needs to be analyzed. The researches show that due to the blocking effect of propylene substation on the combustible gas cloud under north wind, the equivalent stoichiometric cloud mass is higher than that in the southwest wind direction. The blocks in the working area are mainly distributed along the east-west direction, so the peak overpressure of the propylene substation is smaller than that of the control room. There is a linear relationship between the loading vehicles and the explosion overpressure in the control room. With the decrease of the number of loading vehicles, the explosion overpressure decreased significantly. If the number of loading vehicles is not reduced, the brick wall of the existing control room will be broken and collapsed under explosion loading, threatening the safety of personnel in the control room.

MAPPING VELOCITY OF THE POTSDAM GLACIER, EAST ANTARCTICA USING LANDSAT-8 DATA

Abstract. Most of the glaciers have been retreating and thinning globally due to climate change. Glacier velocity is one such important parameter of glacier dynamics, which helps to understand the mass balance. The variations in velocity at different areas of the glacier can be used to identify the zones of ablation and accumulation. Zones of accumulation are identified as areas with higher velocity. This data is useful to incorporate in the glacier mass balance analysis. This study aims to derive the glacier velocity, using feature tracking technique for Potsdam glacier, east Antarctica. Feature tracking is an efficient way to derive glacier velocity, which is based on a cross-correlation algorithm that seeks offsets of the maximal correlation window on repeated satellite images. In this technique, two temporally different images are acquired for the same area and a distinct feature on both images is identified and the velocity is calculated with respect to the movement of that particular feature from one image to the other. Landsat-8 data for the year 2016 was used to derive velocity. Finer resolution promotes better feature tracking so the panchromatic band (band 8) of Landsat-8 OLI with a resolution of 15 m was utilized for deriving velocity. This technique was performed using COSI-Corr module in ENVI. This tool calculates displacement between the east-west and north-south directions, and the resultant velocity is calculated using the displacement in both directions and the temporal difference of two images. The velocity map generated at a resolution of 240 m showed that the resultant velocity ranged between 18.60 and 285.28 ma−1. Bias and root mean square error (RMSE) have been calculated with respect to the point-by-point MEaSUREs data provided by National Snow and Ice Data Centre at 1000 m resolution. The RMSE was found to be 78.06 ma−1 for 2016. The velocity for Potsdam glacier was also pictorially validated with the DGPS measurements from literature.

Effect of nitrogen supply method on root growth and grain yield of maize under alternate partial root-zone irrigation

A field experiment was carried out to investigate effect of nitrogen (N) supply method on root growth and its correlation with the above-ground parts in maize (Zea mays L.) under alternate partial root-zone irrigation (APRI) at Wuwei, northwest China in 2012 and 2014. The treatments included alternate N supply, conventional N supply and fixed N supply under APRI (designated AN, CN and FN, respectively), with an additional CN fertilizer treatment coupled with conventional irrigation (CK). Ridges were built in a west-east direction. Root weight density (RWD) in the 0–100 cm soil layer and shoot biomass at the V6, V12, VT, R2 and R6 stages, and grain yield and yield components at the R6 were determined. Results showed that RWD around the plant (i.e. under the plant, south and north of the plant) in the 0–40 cm soil layer varied among different treatments at the VT, R2 and R6 stages. The RWD north and south the plant were comparable during maize growth stages for AN, CN and CK, while FN significantly decreased the RWD of its no N supply side at the three stages and markedly decreased the RWD of its N supply side at the VT. AN and CN significantly increased the RWD, shoot biomass at the three stages, and grain yield compared with FN and CK. Grain yield was positively correlated with RWD in the 0–40 cm soil layer at the three stages. These results suggested that AN and CN produced a relatively uniform distribution of roots and a greater root biomass, which contributed to the enhanced shoot biomass and grain yield of maize under APRI.

Spatial Distribution Pattern and Prediction of Pension Pressure in Provinces of China

Along with China stepping into the aging society, pension pressure has become a social livelihood issue. This paper firstly defines the concept of pension pressure standing on the employment. On this basis, the research uses the spatial autocorrelation and standard deviation ellipse to study the spatial distribution pattern and evolution characteristics of pension pressure. Furthermore, the study constructs the GM (1,1) model to predict the trend of pension pressure. Based on the data collected from 31 provinces from 1995 to 2016, it found out that the pension pressure in China shows a slow upward trend generally. The growth of the pension pressure has a spatial agglomeration effect, and the pension pressure is characterized by a general pattern of divergent spatial distribution, mainly in the East-West direction and supplemented by the North-South direction. In addition, the future distribution pattern of pension pressure in China will shift from “Northeast to Southwest” to “North to South”, and it will basically become stable in the future.

Upper mantle anisotropy and tectonic deformation beneath the Ordos Block in the western North China Craton: Constraints from wide-angle seismic data

The Ordos Block is located in the northern part of the North China Craton and its interior is highly stable. A series of fault basins and faults has developed around the periphery, and seismic activity is frequent. To research the dynamic mechanisms that caused the special geomorphology and geological features of the Ordos Block further, this study processed data from two nearly orthogonal profiles laid out in this area and obtained the P-wave velocity structure characteristics of the area. The results showed that the crust–mantle velocity structure, interface depth, and the relationship with the peripheral regions obtained from the two profiles are rather complex: the internal crust structure of the Ordos Block is relatively simple, the low-velocity layer is not developed, the interface does not undulate much, and the crust thickness of the Ordos Block is about 42.0 km. These results show that the Ordos Block is part of a sinking residual feature of the ancient stable continental lithosphere. The crust–mantle structure of the block and its peripheral coupled region shows complex crustal structure features. The velocity structure is abnormally disordered and the interface shows declining or depressed anomalies, revealing the background characteristics of the active structure of the block and the periphery. Another major feature is that the velocity of the Pn wave at the uppermost mantle near the intersection of the two profiles has directional and anisotropic features, i.e., the value of the velocity in the east–west direction is significantly greater than that in the north–south direction and the difference is 0.25 km/s. The reason for this phenomenon may be that since the Mesozoic Era the Ordos Block has been mainly subject to east–west compressive stress, forming a series of north–south structural deformations.

Spatiotemporal Variation of Crustal Anisotropy in the Source Area of the 2004 Niigata, Japan Earthquake

AbstractWe investigate the spatiotemporal pattern of crustal anisotropy in the source area of the 2004 Niigata earthquake (M 6.8) that occurred in the northern segment of the Niigata–Kobe tectonic zone, central Japan, by measuring shear‐wave splitting parameters from waveform data of local earthquakes. Our results show that the fast polarization directions in the upper crust have spatial variations across the region of the earthquake that are likely caused by both structural and stress field effects. The northwest–southeast direction near the northeastern end of the source zone (beneath station N.NGOH) and the east–west direction to the southwest (beneath station N.KWNH) are consistent with the spatial variation of the orientation of the maximum compression of the local stress field. Fast polarization directions at other stations tend to align in the directions of active faults and folds and thus are considered to be structure induced. These spatial patterns were unaffected by the earthquake. However, at two stations (N.NGOH and N.KWNH) we observe an increase in both the average and scatter of the normalized delay times (δt) during the aftershock period. In addition, two stations (HIROKA and N.YNTH) that are located in the strike‐normal direction east of the source area show an increase in the average of the normalized δt and a rotation of up to 90° of the fast direction immediately after the mainshock. We also notice that stations located very close to the source fault (DP.YMK and DP.OJK) show larger average delay times compared with stations farther away (HIROKA and N.YNTH) during the postseismic stage. To explain the temporal changes in the strength of the anisotropy, we speculate that spatiotemporal variations in microcrack development in and around the source area could be caused by static stress changes due to tectonic deformation and the earthquake rupture.