On the earthquake effects in the regime of Pc1

While searching for electromagnetic effects of the earthquakes, impulse-type signals in the frequency range of 0–5 Hz preceding the earthquake or following it have been detected. The advance or delay time is from 0 to 5 min. The signals are observed as single or pair impulses. It is supposed that the signals make a significant impact on the state of the magnetosphere and ionosphere. As a result, a sharp change in the regime of Pc1 geomagnetic pulsations is possible. These effects are analyzed on the basis of observations of the geomagnetic pulsations at the Borok Geophysical Observatory.     

Analysis of Signals from an Unique Ground-Truth Infrasound Source Observed at IMS Station IS26 in Southern Germany

Quantitative modeling of infrasound signals and development and verification of the corresponding atmospheric propagation models requires the use of well-calibrated sources. Numerous sources have been detected by the currently installed network of about 40 of the final 60 IMS infrasound stations. Besides non-nuclear explosions such as mining and quarry blasts and atmospheric phenomena like auroras, these sources include meteorites, volcanic eruptions and supersonic aircraft including re-entering spacecraft and rocket launches. All these sources of infrasound have one feature in common, in that their source parameters are not precisely known and the quantitative interpretation of the corresponding signals is therefore somewhat ambiguous. A source considered well-calibrated has been identified producing repeated infrasound signals at the IMS infrasound station IS26 in the Bavarian forest. The source results from propulsion tests of the ARIANE-5 rocket’s main engine at a testing facility near Heilbronn, southern Germany. The test facility is at a range of 320 km and a backazimuth of ~280° from IS26. Ground-truth information was obtained for nearly 100 tests conducted in a 5-year period. Review of the available data for IS26 revealed that at least 28 of these tests show signals above the background noise level. These signals are verified based on the consistency of various signal parameters, e.g., arrival times, durations, and estimates of propagation characteristics (backazimuth, apparent velocity). Signal levels observed are a factor of 2–8 above the noise and reach values of up to 250 mPa for peak amplitudes, and a factor of 2–3 less for RMS measurements. Furthermore, only tests conducted during the months from October to April produce observable signals, indicating a significant change in infrasound propagation conditions between summer and winter months.     

The characteristics of seismic signals produced by lahars and pyroclastic flows: Volcán de Colima,México

The general characteristics of seismic signals produced by pyroclastic flows (generated by either the collapse of a lava dome or an eruptive column) and lahars at Volcán de Colima, México are discussed. The paper concentrates on the 2004–2006 activity associated with and following the extrusion of andesitic block-lava in October–November 2004. It is shown that the duration of the broad-band seismic records of pyroclastic flows lasts a few minutes while the duration of seismic records of lahars continues for tens of minutes or hours. The spectra of seismic records produced by pyroclastic flows are characterized by lower peak frequencies (around 3–4 Hz) than for lahars (around 6–8 Hz). This difference in the frequency content together with the difference in the duration of seismic signals allows early diagnostic of the events in real time.     

Variations in thunderstorm VLF emissions propagating over epicenters of earthquakes

In this study, the variations of average amplitude of the very-low-frequency (VLF) signal thunderstorm origin propagating over areas of strong (magnitude >5) earthquakes are considered. Despite the non-stationary state of thunderstorms, a decrease in the amplitude of its VLF signals was usually detected 3–6 days before an earthquake, with subsequent recovery on the day of the event. The effect is similar to the attenuation of the signal amplitude of low-frequency radio stations that is observed for several days before the occurrence of an earthquake. These influences of earthquakes on thunderstorm VLF signals are recorded along different paths (different azimuths and different distances to the earthquake epicenter). The probability that an earthquake of strong magnitude will induce changes in the thunderstorm VLF signal is 60–70%.     

Detection of wave disturbances in the mesosphere using a MF-HF radar

Theoretical backgrounds of the active and passive methods for detecting the set of acoustic gravity waves in the upper mesosphere are presented. The observation and processing techniques based on the registration, statistical and spectral analysis of the envelopes of backscatter signals and radio noise are presented. It has been indicated that wave disturbances with periods of 5–120 min were observed during the entire observation period. The average relative amplitude of these disturbances was 2–4%. The dependences of the wave disturbance parameters on the time of day, season, and magnetic activity level have been studied.     

Quartz OSL and TL dating of pottery,burnt clay,and sediment from Beicun archaeological site,China

This study focuses on characterizing the thermoluminescence (TL) and optically stimulated luminescence (OSL) of quartz in burnt clay, pottery, and the sediments unearthed from a Neolithic site, the Beicun site of the Liangzhu culture. It shows that the initial OSL signals (within 0.8 s) of most burnt clay and pottery sherds are not dominated by the fast component. Results of a heating simulation experiment of sediment quartz show that annealing at temperatures exceeding 600–800 °C decreased the proportion of the fast component in the initial signal slightly. In addition, the proportion of the medium component in the later signal (0.8–5 s) increased significantly, resulting in a decrease in the Fast Ratio value. Therefore, high annealing temperature may be an important reason for the slow decay rate of OSL signals of the burnt clay and pottery samples. The D_e(t) plot shows that most of the samples have thermally stable OSL component signals, which have no significant effect on the final OSL ages. The single-aliquot regenerative-dose (SAR) protocol was used to determine the OSL and TL ages for chunk burnt clay and pottery sherds. The high-precision age of the last archaeological heating event, such as sacrifice, burning, or domestic firing, can be obtained by determining the TL and OSL ages of a homogeneous chunk of burnt clay. The OSL results are consistent with the ¹⁴C age of carbon chips extracted from burnt clay. The age of the Beicun site is finally determined to be approximately 5000–5300 BP (BP represents before 2020), belonging to the early period of the Liangzhu culture.     

泰安重力观测高频波动信号分析

系统分析了泰安重力观测资料正常和异常时信号的周期特征,研究了高频异常信号与台风、气压和强震之间的关系.结果表明:泰安重力观测正常时信号周期为2～4分钟,异常时信号周期只有2～3分钟,异常信号幅值约为正常信号的5倍;高频异常信号主要是由西太平洋洋面上生成的进入中国大陆或近海的台风引起的,占台风引起泰安重力出现高频异常信号的90%;重力高频信号与台风中心速度正相关,与台风距离负相关,并且随台风的结束高频信号也随之消失;少数高频异常信号与强震也有一定关系,占地震总数的17.24%;高频异常信号与气压变化无关.     

Extending the age limit of luminescence dating using the dose-dependent sensitivity of MET-pIRIR signals from K-feldspar

We investigated the sensitivity change of multiple-elevated-temperature (MET) stimulated post-infrared infrared-stimulated luminescence (MET-pIRIR) signals as a response to irradiation, sunlight bleaching and heating using samples from the Mu Us Desert, central China. A strong dose dependence of MET-pIRIR signal sensitivity was observed. The intensity of the test-dose signals (T_x) increase with the pre-dose received. Furthermore, the signal sensitivity can be reset by sunlight bleaching or heating. This suggests that both the electron traps and hole centres in K-feldspar can be bleached by sunlight, and can, therefore, be used for dating. Using the test-dose signal as a monitor for sensitivity change, it was found that the sensitivity (or hole centres) saturate at a higher dose (D₀ = ∼750 Gy) than the sensitivity-corrected signals (or electron traps) (D₀ = ∼400 Gy). We propose a multi-aliquot regenerative-dose (MAR) MET-pIRIR dating protocol, which utilises the high saturation dose of hole centres. This protocol was tested using aeolian sediments from north China with ages ranging from 0 to 470 ka. It was found that, compared to the dose limit of ∼800–1000 Gy using the normal MET-pIRIR or pIRIR procedure, the new method can measure a natural dose of up to ∼1500 Gy and produce ages consistent with the expected ages for the samples investigated.     

Estimating Global Energy Flow from the Global Upper Ocean

The relative significance of short multi-year linear trends in the global integral of 0–700?m ocean heat content anomaly (OHCA) is investigated by examining the overlapping segments of the 16-year OHCA curve from Lyman et al. (Nature 465:334–337, 2010). Segments of 4 years and less are found not to be significantly different from each other or from 0 at the 90% confidence interval. Likewise, short 5- to 7-year segments are not statistically different from each other. Ten-year and longer trends are significant and provide a useful comparison for satellite observations of the radiation imbalance at the top of the atmosphere.     

Some results of observations of positive lightning discharges and relative phenomena in the east of Siberia

We have considered spatial distributions of positive lightning discharges in the east of Siberia for the summer seasons of 2003–2007 and properties of their electromagnetic signals with the ELF “slow tail”, which, as is known, can be accompanied by sprites. There are two main regions of positive discharges located in the south and west of Yakutsk. Two other “centers” (the northeastern and the eastern) are located in high-mountainous regions. In these regions the positive discharges intensity can exceed the negative discharge intensity.The electromagnetic signals in the ELF range (usually in the form of two half-cycles) were observed after the VLF atmospherics were recorded in the high-latitude regions. The delay of ELF pulses relative to the corresponding atmospherics was 0–7 ms. The long (up to 350 ms) events of quasi-periodic ELF oscillations with the period of about 7 ms (which corresponds to the quasi-period of ELF pulses) were revealed.     

Relationship between soil moisture of near surface and multiple depths of the root zone under heterogeneous land uses and varying hydroclimatic conditions

This paper presents an assessment of the relationship between near-surface soil moisture (SM) and SM at other depths in the root zone under three different land uses: irrigated corn, rainfed corn and grass. This research addresses the question whether or not near-surface SM can be used reliably to predict plant available root zone SM and SM at other depths. For this study, a realistic soil-water energy balance process model is applied to three locations in Nebraska representing an east-to-west hydroclimatic gradient in the Great Plains. The applications were completed from 1982 through to 1999 at a daily time scale. The simulated SM climatologies are developed for the root zone as a whole and for the five layers of the soil profile to a depth of 1·2 m. Over all, the relationship between near-surface SM (0–2·5 cm) and plant available root zone SM is not strong. This applies to all land uses and for all locations. For example, r estimates range from 0·02 to 0·33 for this relationship. Results for near-surface SM and SM of several depths suggest improvement in r estimates. For example, these estimates range from − 0·19 to 0·69 for all land uses and locations. It was clear that r estimates are the highest (0·49–0·69) between near-surface and the second layer (2·5–30·5 cm) of the root zone. The strength of this type of relationship rapidly declines for deeper depths. Cross-correlation estimates also suggest that at various time-lags the strength of the relationship between near-surface SM and plant available SM is not strong. The strength of the relationship between SM modulation of the near surface and second layer over various time-lags slightly improves over no lags. The results suggest that use of near-surface SM for estimating SM at 2·5–30 cm is most promising. Copyright © 2007 John Wiley & Sons, Ltd.     

Late Quaternary lake level record of Orog Nuur,southern Mongolia,revealed by optical dating of paleo-shorelines

The Late Quaternary hydroclimatic evolution of lake systems in Mongolia remains unclear. Here we present a record of lake level variations at Orog Nuur in the Valley of Gobi Lakes in southern Mongolia, since the last interglaciation, based on paleo-shoreline dating using quartz optically stimulated luminescence (OSL) and K-feldspar post-infrared infrared stimulated luminescence (pIRIR) signals. Due to feldspar contamination that could not be eliminated, the OSL signals of quartz single-aliquots (SA), except for two Holocene samples, were unsuitable for dating and a double SA regenerative-dose (SAR) protocol was used for the quartz fraction of these two samples. The pIR₅₀IR₁₇₀ and pIR₂₀₀IR₂₉₀ signals of K-feldspar SA were used to date Holocene samples and old samples (>100 ka), respectively, with the SAR protocol. To determine the bleaching condition of the pIR₂₀₀IR₂₉₀ signals, the first pIRIR dating of K-feldspar single-grains of lake shoreline sediments in Mongolia was performed. The equivalent doses of K-feldspar grains show normal distributions, suggesting that the pIR₂₀₀IR₂₉₀ signals are well-bleached. Overall, the results, combined with those of previous studies, show that a mega-lake developed at 56 m above the modern lake level (a.m.l.) during MIS 5e (124.2 ± 6.8–114.7 ± 8.0 ka). Holocene high-stands occurred in the last deglaciation–early Holocene (11.1 ± 1.0 ka) at 23 m a.m.l. and in the mid-Holocene (6.7 ± 0.8–3.3 ± 0.4 ka) at 20–14 m a.m.l. The dimensions of the paleo-lakes were recovered, and a hydrological index indicates that the effective moisture during MIS 5e and the mid-Holocene was 10.7 times and 3.6–5.0 times larger than today, respectively. Finally, the possible mechanisms behind the lake level history are discussed based on correlation with independent paleoclimatic records.     

Soil moisture–temperature relationships: results from two field experiments

This paper analyses data from two field experiments in Chickasha, Oklahoma, and Tifton, Georgia, carried out in July 1999 and June 2000 respectively. The observations on soil moisture at two depths, viz. 0–2·5 and 0–5·0 cm, surface temperature, and temperatures at 1, 5 and 10 cm depths are analysed. The relationship between the soil moisture and the temperature variability in time is examined as a function of vegetation type and location. Results from these experiments show that, during drydown, surface temperature shows an increase that corresponds to a decrease in the soil moisture. Linear models for prediction of soil moisture (at both depths) using surface temperature observations are examined. Copyright © 2003 John Wiley & Sons, Ltd.     

Lunar seismicity and tectonics

Seismic signals from 300–700 deep moonquakes and about four shallow moonquakes are detected by the long-period seismometers of two or more of the Apollo seismic stations annually. Deep-moonquake activity detected by the Apollo seismic network displays tidal periodicities of 0.5 and 1 month, 206 d and 6 a. Repetitive moonquakes from 60 hypocenters produce seismograms characteristic of each. At each hypocenter, moonquakes occur only within an active period of a few days during a characteristic phase of the monthly lunar tidal cycle. An episode of activity may contain up to four quakes from one hypocenter. Nearly equal numbers of hypocenters are active at opposite phases of the monthly cycle, accounting for the 0.5-month periodicity. The 0.5- and 1-month activity peaks occur near times of extreme latitudinal and longitudinal librations and earth-moon separation (EMS). The 206-d and 6-a periodicities in moonquake occurrence and energy release characteristics are associated with the phase variations between the librations and EMS. Because of the exact relationship between tidal phases and the occurrence of deep moonquakes from a particular hypocenter, it is possible to predict not only the occurrence times from month to month, often to within several hours, but also the magnitudes of the moonquakes from that hypocenter. The predicted occurrence of large A₁ moonquakes in 1975, following a 3-a hiatus, confirms the correlation between A₁-moonquake activity and the 6-a lunar tidal cycle and implies a similar resurgence for all of the deep moonquakes. Because no matching shallow moonquake signals have been identified to date, tidal periodicities cannot be identified for the individual sources. However, shallow moonquakes generally occur near the times of extreme librations and EMS and often near the same tidal phase as the closest deep moonquake epicenters. With several possible exceptations, the deep-moonquake foci located to date occur in three narrow belts on the nearside of the moon. The belts are 100–300 km wide, 1,000–2,500 km long and 800–1,000 km deep and define a global fracture system that intersects in central Oceanus Procellarum. A fourth active, although poorly defined, zone is indicated. The locations of 17 shallow-moonquake foci, although not as accurate as the deep foci, show fair agreement with the deep-moonquake belts. Focal depths calculated for the shallow moonquakes range from 0–200 km. Deep-moonquake magnitudes range from 0.5 to 1.3 on the Richter scale with a total energy release estimated to be about 10¹¹ erg annually. The largest shallow moonquakes have magnitudes of 4–5 and release about 10¹⁵–10¹⁸ erg each. Tidal deformation of a rigid lunar lithosphere overlying a reduced-rigidity asthenosphere leads to stress and strain concentrations near the base of the lithosphere at the level of the deep moonquakes. Although tidal strain energy can account for the deep moonquakes in this model, it cannot account for the shallow moonquakes. The tidal stresses within the lunar lithosphere range from about 0.1 to 1 bar and are insufficient to generate moonquakes in unfractured rock, suggesting that lunar tides act as a triggering mechanism. The largest deep moonquakes of each belt usually occur near the same characteristic tidal phases corresponding to near minimum or maximum tidal stress, increasing tidal stress, and alignments of tidal shear stresses that correspond to thrust faulting along planes parallel to the moonquake belts and dipping 30–40°. With few exceptions, the shallow moonquakes occur at times of near minimum tidal stress conditions and increasing tidal stress that also suggest thrust faulting. The secular accumulation of strain energy required for the shallow moonquakes and implied by the uniform polarities of the deep moonquake signals probably results from weak convection. A convective mechanism would explain the close association between moonquake locations and the distribution of filled mare basins and thin lunar crust, the earth-side topographic bulge, and the ancient lunar magnetic field. The low level of lunar seismic activity and the occurrence of thrust faulting both at shallow and great depths implies that the moon is presently cooling and contracting at a slow rate.     

A field‐based investigation to examine underwater soundscapes of five common river habitats

Aquatic river habitat types have been characterized and classified for over five decades based on hydrogeomorphic and ecological variables. However, few studies considered the generation of underwater sound as a unique property of aquatic habitats, and therefore as a potential information source for freshwater organisms. In this study, five common habitat types along 12 rivers in Switzerland (six replicates per habitat type) were acoustically compared. Acoustic signals were recorded by submerging two parallel hydrophones and were analysed by calculating the energetic mean as well as the temporal variance of ten octave bands (31·5 Hz–16 kHz). Concurrently, each habitat type was characterized by hydraulic and geomorphic variables, respectively. The average relative roughness, velocity‐to‐depth ratio, and Froude number explained most of the variance of the acoustic signals created in different habitat types. The average relative roughness predominantly affected middle frequencies (63 Hz–1 kHz), while streambed sediment transport increased high‐frequency sound pressure levels (2–16 kHz) as well as the temporal variability of the recorded signal. Each aquatic habitat type exhibited a distinct acoustic signature or soundscape. These soundscapes may be a crucial information source for many freshwater organisms about their riverine environment. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of the total solar eclipse of March 20, 2015, on VLF/LF propagation

The analyzed amplitude and phase variations in electromagnetic VLF and LF signals at 20–45 kHz, received in Moscow, Graz (Austria), and Sheffield (UK) during the total solar eclipse of March 20, 2015, are considered. The 22 analyzed paths have lengths of 200—6100 km, are differently oriented, and cross 40–100% occultation regions. Fifteen paths crossed the region where the occultation varied from 40 to 90%. Solar eclipse effects were found only on one of these paths in the signal phase (–50°). Four long paths crossed the 90–100% occultation region, and signal amplitude and phase anomalies were detected for all four paths. Negative phase anomalies varied from–75° to–90°, and the amplitude anomalies were both positive and negative and were not larger than 5 dB. It was shown that the effective height of the ionosphere varied from 6.5 to 11 km during the eclipse.     

Tomographic imaging of the ionosphere using the GPS/MET and NNSS data

The earlier experiments of ionospheric tomography were conducted by receiving satellite signals from ground-based stations and then reconstructing electron density distribution from measures of the total electron content (TEC). In June 1994, National Central University built up the low-latitude ionospheric tomography network (LITN) including six ground stations spanning a range of 16.7° (from 14.6°N to 31.3°N) in latitude within 1° of 121°E longitude to receive the naval navigation satellite system (NNSS) signals (150 and 400 MHz). In the study of tomographic imaging of the ionosphere, TEC data from a network of ground-based stations can provide detailed information on the horizontal structure, but are of restricted utility in sensing vertical structure. However, an occultation observation mission termed the global positioning system/meteorology (GPS/MET) program used a low Earth orbiting (LEO) satellite (the MicroLab-1) to receive multi-channel GPS carrier phase signals (1.5 and 1.2 GHz) and demonstrate active limb sounding of the Earth's atmosphere and ionosphere. In this paper, we have implemented the multiplicative algebraic reconstruction technique (MART) to reconstruct and compare two-dimensional ionospheric structures from measured TECs through the receptions of the GPS signals, the NNSS signals, and/or both of the systems. We have also concluded the profiles retrieved from tomographic reconstruction showing much reasonable electron density results than the original vertical profiles retrieved by the Abel transformation and being in more agreement in peak electron density to nearby ionosonde measurements.     

Investigation of karstic hydrological processes of Niangziguan Springs (North China) using wavelet analysis

Niangziguan Spring complex is the largest karst spring in North China. We investigate the karst hydrological processes by using Morlet wavelet transform analysis and cross wavelet analysis based on monthly precipitation from 1958 to 2010 and spring discharge from 1958 to 2009. From Morlet wavelet transform coefficients of precipitation and the spring discharge in Niangziguan Springs Basin, we find that the precipitation and discharge are characterized by the multi‐scale features in the time domain, and the energy distribution of the signal is highly irregular across scales. Although precipitation eventually becomes spring discharge by infiltrating and propagating through karst formations, the signals are attenuated. The results also show that the precipitation of Niangziguan Springs Basin has the main periodic components of 1‐, 5‐, 12‐, and 17‐year periods with alternating wet–drought cycle. Similarly, the spring discharge of Niangziguan Springs has the main components of 17‐year periods, but the 1‐, 5‐, and 12‐year periodicity of precipitation are not reflected in spring discharge, which is filtered by the aquifers. The results of cross wavelet analysis reveal that the precipitation and spring discharge share the common periodicity of 17 years. This means that those signals with high energy and long timescales can penetrate through the aquifer and be reflected in spring discharge, whereas other signals are filtered and modified. Copyright © 2011 John Wiley & Sons, Ltd.     

利用VP型垂直摆倾斜仪观测数据检测2011日本M_w9.0级地震激发的低频地球自由振荡

甚长周期VP型垂直摆倾斜仪对某些地球物理信号有特殊的敏感性,除了在观测小地震、慢地震等方面有优势之外,还可有效应用于低频地球自由振荡信号的探测.利用安置在武汉大学珞珈山的我国自行研制的VP型垂直摆倾斜仪在2011日本Mw9.0级大地震之后不同长度的观测数据,联合EEMD方法、自回归估计(AR)方法和bootstrap法,本文不仅检测到该地震激发的频率小于4.7 mHz的零阶球型振荡(0S2至0S38)和环型振荡(0T4至0T35)几乎所有振型以及15个谐频振型,还检测到5个其频率低于1mHz的低阶球型多线态(0S2、2S1、0S3、0S4和1S2)的部分或全部谱峰分裂现象,并给出了所有检测结果的精度评估.此外,本文分析了某些球型和环型振荡之间的耦合效应,结果表明耦合效应将显著影响地球自由振荡信号的相关参数.