ALBERT

Description: Abstract Whistler mode waves, particularly rising tone emissions, are important for nonlinear interactions with energetic electrons in the Earth's magnetosphere. In this letter, we evaluate the characteristics of rising tone whistler mode waves in three distinct regions: 1. inside the plasmasphere; 2. plasmapheric plumes, and 3. plasmatrough (outside the plasmapause). Our statistical results indicate that the occurrence rate of rising tone emissions tends to increase with increasing geomagnetic activity and is highest in plasmaspheric plumes among these three regions. Inside the plasmasphere, rising tone emissions typically occur in the outer portion of the plasmasphere, particularly near the dawnside. Moreover, the rising tone emissions inside the plasmasphere and plumes tend to be more field aligned than those in the plasmatrough. Our new findings of global wave properties of rising tone emissions are critical for understanding the generation of rising tone emissions and their effects on radiation belt electron dynamics.

Description: 〈span〉〈div〉Abstract〈/div〉Earthquake insurance has become a topic of major importance in mainland China ever since the Mw 7.9 Wenchuan earthquake in 2008. Site‐condition amplification is one of the essential factors that influences the prediction of strong ground motion and the assessment of damages of buildings and structures. The site effects should hence be included in calculating earthquake damage and determining the insurance rate for insurance companies. In particular, large‐scale site classification is required for the implementation of earthquake insurance. This study first used a slope method for site classification in China through the VS30 values from the topographic slope data and the correlation between VS30 and the topographic slope. A novel site classification method, called the slope–geological method, was then proposed in this study to improve the slope method by combining geological characteristics, including geological age, the depositional environment, and soil properties. Four hundred and fifty three pieces of borehole data in Northern Plain and Sichuan of China were used to verify the effectiveness and difference of the slope method and the slope–geological method proposed in this study. Site‐condition classification maps of China were drawn using the slope method and slope–geological method, respectively.〈/span〉

Description: Abstract Seismic spectral ratios between the 3 September 2017 North Korean nuclear test (NKT2017) and four earlier Korean tests (25 May 2009, NKT2009; 12 February 2013, NKT2013; 6 January 20016, NKT2016J; and 9 September 2016, NKT2016S) are investigated. All the observed teleseismic P wave spectral ratios exhibit a unique notch at approximately 2.5 Hz, but it is not observed for spectral ratios of regional P and Lg waves. Meanwhile, for a given event pair, the network‐averaged Lg wave spectral ratio is similar to that of regional P wave, but with the explosions' source corner frequencies significantly reduced, supporting the conjecture by Fisk (2006, https://doi.org/10.1785/0120060023). We demonstrated that the observed notch of teleseismic P wave spectral ratios may be well modeled with interference between pP and P waves with an apparent pP‐P time delay ΔtpP of about 0.4 s for NKT2017, while regional P wave spectral ratios may be well fitted with source spectral ratios predicted by classical explosion source models including Mueller and Murphy (1971, https://doi.org/10.2172/4107998) (MM71), Denny and Johnson (1991, https://doi.org/10.1029/gm065p0001) (DJ91), and their two hybrids. Via the above modeling, yield sizes of the explosions and the depth of burials of NKT2009–2016S are determined as functions of NKT2017's buried depth h0. Our result indicate that, for h0 in the range of 600–1,100 m, the MM71‐related models give yield estimations about 100–300 kt for NKT2017, 3–7 kt for NKT2009, 6–15 kt for NKT2013 and NKT2016J, and 10–25 kt for NKT2016S, while yield sizes obtained by model DJ91 are much smaller. Nevertheless, for all the above source models, the obtained depths of burial estimations of NKT2009–2016S are always significantly smaller than NKT2017's depth of burial h0.

Description: Based on the parallel computing cluster platform of the ABAQUS software, a large-scale 2D finite-element refined nonlinear modeling approach was used to study seismic site effects in the Fuzhou basin, such as peak ground acceleration (PGA), spectral acceleration, duration, and acceleration transfer functions. A 1D equivalent linear wave propagation analysis was conducted also, with Proshake for supplementation and calibration. The simulation results demonstrated the following. (1) PGA amplification factors exhibited spatial variation characteristics that varied both laterally and with depth and exhibited a nonmonotonic decreasing characteristic with soil depth. From the 2D results, a greater motion amplification and focusing effect for some shallow soil layers was observed where there was significant fluctuation of the underlying bedrock interface. The moderate- and long-period ground-motion components were obviously amplified, but were was less pronounced in the 1D result. (2) For low-, moderate-, and high-level earthquakes, the surface PGA amplification factors were 1.4–2.5, 1.3–2.0, and 1.1–2.0, respectively, and the predominant periods of the basin were 0.35–0.65 s, 0.40–0.75 s, and 0.50–1.05 s, respectively. (3) Ground-motion durations were prolonged to different degrees, which were closely related to the characteristics of seismic bedrock motions. (4) The sensitive frequency band of the seismic site response was from 0.5 to 2 Hz. (5) Ground-motion amplification in the downtown section of the city of Fuzhou was generally larger. To a certain extent, the 2D results reflect the influences of the surface topography relief, the fluctuation of the underlying bedrock interface, and lateral heterogeneity of soils on seismic-wave propagation.

Description: Striking networks of livestock tracks, or terracettes, molded to the contours are a common feature on hilly rangelands of the semiarid Loess Plateau, one of the regions with the most severe soil erosion in the world. The formation of livestock tracks results in modified micro-topography and ecological processes and leads to strong patterns in spatial distribution of vegetation, water, and nutrients. We investigated the spatial pattern of the topo-edaphic, hydrological, biogeochemical, and biological attributes of these terracette landscapes and explored their potential implications to ecosystem functions. The results showed strong spatial heterogeneity in topo-edaphic and biological structure of these landscapes, organized with three segments of a basic landscape unit—track, shoulder, and interslope. The above- and below-ground biomass and soil nutrients concentrated in the shoulder segment forming a “band of fertility”. The network of livestock tracks likely reduced surface runoff and erosion by intercepting runoff and facilitate infiltration, while posing little risk of increasing shallow slope failures given the structure of loess soil. There appears a positive feedback loop for maintaining the structure of terracette landscapes. Trampling by goats maintains the tracks, which leads to spatial heterogeneity in biophysical structure and processes. The network of tracks enabled the goats to travel and graze in ways that reduce energy expenditure and increase foraging efficiency, which leads to strongly preferential use of the tracks by the goats. There are also evidence of a possible process resemble a slope parallel retreat at a micro-scale, which may result in upslope movement of the terracettes. There may be important functional differences between landscapes with and without networks of livestock tracks, in regulating water runoff and soil erosion, forage production, and soil carbon storage. These functional differences may have significant implications to land use policies and practices aiming at soil and water conservation and socioecological sustainability of the Loess Plateau.

Description: The M w  7.0 Kumamoto, Japan, earthquake occurred on 15 April 2016 at 16:25 UTC. Using ground accelerations recorded by 104 near-field stations, we investigate spatial variability of observed ground motions, apparent period dependence, and azimuthal variation, as well as rupture directivity effects on various intensity measures. We develop a simplified ground-motion model that includes both geometric and anelastic attenuation terms. Comparisons of observed and predicted ground motions suggest that predictions from the Next Generation Attenuation-West2 models provide good fits for the overall observation. Analysis of spatial distribution of the residuals shows that observed peak ground velocity (PGV) and long-period spectral accelerations (SAs) in the 150°–180° azimuth range along the rupture backward direction (southwest of the fault) can be as low as 0.3–0.8 times the average observation of this event. Long-period ground motions on the northeast side of the fault in the forward direction are much higher than average, with PGV and long-period SAs ranging from 1.2 to 1.5 times the average. There is clear period dependence of the strong ground motion variation. The biases due to directivity generally decrease with decreasing period for all azimuth ranges. On the distance dependence of directivity effects, our study shows that directivity effects can be considered practically nonsignificant for stations close to the hypocenter. We also perform a log–linear regression of the residuals, using a new directivity predictor. Our results show that for the 2016 M w  7.0 Kumamoto earthquake, rupture directivity produces significant amplifications in the rupture forward direction, whereas deamplification effects are observed in the rupture backward region. Directivity effects are particularly relevant for PGV and long-period SA (i.e., SA at periods ≥2.0 s). Such effects do not have systematic influence on peak ground acceleration and short-period ground motions (i.e., SA at periods 〈2.0 s). Electronic Supplement: Figures of variation of regression residuals with R rup for observed peak ground acceleration (PGA), peak ground velocity (PGV), and spectral accelerations (SAs) and of regression residuals versus V S 30 .

Description: The formation and variability of the Van Allen radiation belts are highly influenced by charged particles accelerated via drift-resonant interactions with ultralow frequency (ULF) waves. In the prevailing theory of drift resonance, the ULF wave amplitude is assumed independent of magnetic longitude. This assumption is not generally valid in Earth's magnetosphere, as supported by numerous observations that point to the localized nature of ULF waves. Here, we introduce a longitude dependence of the ULF wave amplitude, achieved via a von Mises function, into the theoretical framework of ULF wave-particle drift resonance. To validate the revised theory, the predicted particle signatures are compared with observational data through a best-fit procedure. It is demonstrated that incorporation of non-local effects in drift-resonance theory provides an improved understanding of charged particle behavior in the inner magnetosphere through the intermediary of ULF waves.

Description: Earthquake ground-motion prediction models usually define site conditions based on the time-averaged shear-wave velocity in the upper 30 m ( V S 30 ). Proxy-based estimations of V S 30 are commonly used, if velocity measurements are not available. We compile a soil-profile database for the Beijing plain area (China), using data from research documents and technical reports. The database contains 479 soil profiles, 463 of which have depths greater than 30 m. We develop regional relationships for the Beijing plain area for extrapolating the time-averaged shear-wave velocity to a given depth less than 30 m to V S 30 , and then compare the performance of available models. We find that the second-order polynomial model ( Boore et al. , 2011 ), based on data from Japan, provides an overprediction, whereas the linear model ( Boore, 2004 ) calibrated on data from California underestimates V S 30 . We develop relationships for estimating V S 30 based on proxies such as ground slope gradients from radar-derived digital elevation models (DEMs) and surface geology at different scales. We find that local V S 30 data in the Beijing plain are generally lower than existing 30 arcsec gradient-based global models. Regression results show a modest correlation between V S 30 and topographic ground slope for several DEM resolutions (3, 15, 30, and 60 arcsec). Geology-based proxies are more effective than ground slope for V S 30 estimation in the analyzed area. We propose a bilinear model based on geologic ages and depositional environments for estimating V S 30 , which shows a statistically significant trend for application in the Beijing plain area. Online Material: Figures showing topographic ground slopes and correlations of V S 30 with topographic slope from digital elevation model (DEM) data and a table summarizing data from the 463 boreholes.

Description: 〈span〉〈div〉Abstract〈/div〉Earthquake insurance has become a topic of major importance in mainland China ever since the Mw 7.9 Wenchuan earthquake in 2008. Site‐condition amplification is one of the essential factors that influences the prediction of strong ground motion and the assessment of damages of buildings and structures. The site effects should hence be included in calculating earthquake damage and determining the insurance rate for insurance companies. In particular, large‐scale site classification is required for the implementation of earthquake insurance. This study first used a slope method for site classification in China through the VS30 values from the topographic slope data and the correlation between VS30 and the topographic slope. A novel site classification method, called the slope–geological method, was then proposed in this study to improve the slope method by combining geological characteristics, including geological age, the depositional environment, and soil properties. Four hundred and fifty three pieces of borehole data in Northern Plain and Sichuan of China were used to verify the effectiveness and difference of the slope method and the slope–geological method proposed in this study. Site‐condition classification maps of China were drawn using the slope method and slope–geological method, respectively.〈/span〉