Short-term Anomaly Research Articles

KMT-2023-BLG-1866Lb: Microlensing super-Earth around an M dwarf host

Aims. We aim to investigate the nature of the short-term anomaly that appears in the lensing light curve of KMT-2023-BLG-1866. The anomaly was only partly covered due to its short duration of less than a day, coupled with cloudy weather conditions and a restricted nighttime duration. Methods. Considering the intricacy of interpreting partially covered signals, we thoroughly explored all potential degenerate solutions. Through this process, we identified three planetary scenarios that account for the observed anomaly equally well. These scenarios are characterized by the specific planetary parameters: (s, q)inner = [0.9740 ± 0.0083, (2.46 ± 1.07) × 10−5], (s, q)intermediate = [0.9779 ± 0.0017, (1.56 ± 0.25) × 10−5], and (s, q)outer = [0.9894 ± 0.0107, (2.31 ± 1.29) × 10−5], where s and q denote the projected separation (scaled to the Einstein radius) and mass ratio between the planet and its host, respectively. We identify that the ambiguity between the inner and outer solutions stems from the inner-outer degeneracy, while the similarity between the intermediate solution and the others is due to an accidental degeneracy caused by incomplete anomaly coverage. Results. Through Bayesian analysis utilizing the constraints derived from measured lensing observables and blending flux, our estimation indicates that the lens system comprises a very-low-mass planet orbiting an early M-type star situated approximately (6.2–6.5) kpc from Earth in terms of median posterior values for the different solutions. The median mass of the planet host is in the range of (0.48–0.51) M⊙, and that of the planet’s mass spans a range of (2.6–4.0) ME, varying across different solutions. The detection of KMT-2023-BLG-1866Lb signifies the extension of the lensing surveys to very-low-mass planets that have been difficult to detect in earlier surveys.

AI-Based Well-Integrity Monitoring Shows Promise

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 211093, “Development of an Artificial-Intelligence-Based Well-Integrity Monitoring Solution,” by Prihandono Aditama, SPE, Tina Koziol, and Meindert Dillen, Wintershall Dea. The paper has not been peer reviewed. _ This paper presents the proof of concept (PoC) of artificial intelligence (AI)-based well-integrity monitoring for gas-lift, natural-flow, and water-injector wells. AI-model prototypes were built to detect annulus leakage as incident-relevant anomalies from time-series sensor data. The AI models for gas-lift and natural-flow wells achieved a sufficient level of performance, with a minimum of 75% of historical events detected and less than one false positive per month per well. Problem Statement In the exploration and production industry, historical well-integrity events are rare because systems are designed as robustly as possible to prevent incidents. For the authors’ study, there were only 12 historical wellbore leakage incidents spanning 13 years of well operations in the assets considered. The events were treated separately for each well type. This challenge is normally known as anomaly detection and has been studied in various fields where time-series data are used. For a historical incident, two types of anomalies were identified: - Short-term incident relevant anomaly (SIRA), an anomaly occurring within 1 day - Long-term incident relevant anomaly (LIRA), an anomaly lasting for more than 1 day Objective and Success Criteria The primary objective of the PoC was to validate the hypothesis that incident-relevant anomalies from historical well-sensor data can be predicted and monitored by using adequate AI models. A generalized AI model was built so that it would detect a well-annulus leakage in future wells. Success criteria were defined by two approaches: a human-centric approach and a statistical approach. For the human-centric approach, the future users were interviewed to obtain insights about their requirements for tool performance. The feedback was mapped against a confusion matrix. Users preferred to optimize the number of correctly predicted historical incidents (true positives) while achieving an acceptable number of false positives. In general, wrong predictions were seen as acceptable (false positives) to a certain degree, depending on the number of wells under a user’s responsibility. Based on those insights, the AI model was optimized for recall instead of precision. Recall (sometimes known as sensitivity) is defined as the number of true positives divided by the total of true positives and false negatives and measures the miss rate. The tradeoff for choosing this approach means the AI model will report some false alarms.

KMT-2021-BLG-1150Lb: Microlensing planet detected through a densely covered planetary-caustic signal

Aims. Recently, there have been reports of various types of degeneracies in the interpretation of planetary signals induced by planetary caustics. In this work we check whether such degeneracies persist in the case of well-covered signals by analyzing the lensing event KMT-2021-BLG-1150, the light curve of which exhibits a densely and continuously covered short-term anomaly. Methods. In order to identify degenerate solutions, we thoroughly investigated the parameter space by conducting dense grid searches for the lensing parameters. We then checked the severity of the degeneracy among the identified solutions. Results. We identify a pair of planetary solutions resulting from the well-known inner-outer degeneracy, and find that interpreting the anomaly is not subject to any degeneracy other than the inner-outer degeneracy. The measured parameters of the planet separation (normalized to the Einstein radius) and mass ratio between the lens components are (s, q)in ~ (1.297, 1.10 × 10−3) for the inner solution and (s, q)out ~ (1.242, 1.15 × 10−3) for the outer solution. According to a Bayesian estimation, the lens is a planetary system consisting of a planet with a mass Mp = 0.88−0.36+0.38 Mj and its host with a mass Mh = 0.73−0.30+0.32 M⊙ lying toward the Galactic center at a distance DL = 3.8−1.2+1.3 kpc. By conducting analyses using mock data sets prepared to mimic those obtained with data gaps and under various observational cadences, we find that gaps in data can result in various degenerate solutions, while the observational cadence does not pose a serious degeneracy problem as long as the anomaly feature can be delineated.

KMT-2021-BLG-1898: Planetary microlensing event involved with binary source stars

Aims. The light curve of the microlensing event KMT-2021-BLG-1898 exhibits a short-term central anomaly with double-bump features that cannot be explained by the usual binary-lens or binary-source interpretations. With the aim of interpreting the anomaly, we analyze the lensing light curve under various sophisticated models. Methods. We find that the anomaly is explained by a model, in which both the lens and source are binaries (2L2S model). For this interpretation, the lens is a planetary system with a planet/host mass ratio of q ~ 1.5 × 10−3, and the source is a binary composed of a turn off or a subgiant star and a mid K dwarf. The double-bump feature of the anomaly can also be depicted by a triple-lens model (3L1S model), in which the lens is a planetary system containing two planets. Among the two interpretations, the 2L2S model is favored over the 3L1S model not only because it yields a better fit to the data, by ∆χ2 = [14.3−18.5], but also the Einstein radii derived independently from the two stars of the binary source result in consistent values. According to the 2L2S interpretation, KMT-2021-BLG-1898 is the third planetary lensing event occurring on a binary stellar system, following MOA-2010-BLG-117 and KMT-2018-BLG-1743. Results. Under the 2L2S interpretation, we identify two solutions resulting from the close-wide degeneracy in determining the planet-host separation. From a Bayesian analysis, we estimate that the planet has a mass of ~0.7−0.8 MJ, and it orbits an early M dwarf host with a mass of ~0.5 M⊙. The projected planet-host separation is ~1.9 AU and ~3.0 AU according to the close and wide solutions, respectively.

ALADDIn: Autoencoder-LSTM-Based Anomaly Detector of Deformation in InSAR

In this study, we address the challenging problem of automatic detection of transient deformation of the Earth’s crust in time series of differential satellite radar [interferometric synthetic aperture radar (InSAR)] images. The detection of these events is important for a wide range of natural hazard and solid earth applications, and InSAR is an ideal data source for this purpose due to its frequent and global observational coverage. However, the size of this dataset precludes a systematic manual analysis, and a low signal-to-noise ratio makes this task difficult. We present a novel method to address this problem. This approach requires the development of a novel network architecture to take advantage of the unique structure of the InSAR dataset. Our unsupervised deep learning model learns the “normal” unlabeled spatiotemporal patterns of background noise signals in 3-D InSAR datasets and learns the relationship between the input difference images and the underlying unknown set of individual 2-D fields of noise from which the InSAR images are constructed. The detection head of our pipeline consists of two complementary methods, semivariogram analysis and density-based clustering. To evaluate, we test and compare three increasingly complex network architectures: compact, deep, and bi-deep. The analysis demonstrates that the bi-deep architecture is the most accurate, and so it is used in the final detection pipeline [autoencoder long short-term memory-based anomaly detector of deformation in InSAR (ALADDIn)]. The analysis of experimental results is based on the detection of a synthetic deformation test case, achieving a 91.25% overall performance accuracy. Furthermore, we show that the ALADDIn can detect a real earthquake of magnitude 5.7 that occurred in 2019 in southwest Turkey.

The reference dependency of short-term reversal

The short-term reversal anomaly has been believed to be compensation for liquidity provision. We put forth the hypotheses that i) liquidity provision for a stock increases with the stock's capital gains overhang and ii) short-term reversal is more pronounced for the stocks with a large capital loss overhang. Our empirical findings support our hypotheses and the results hold firmly, even after we control for risk as well as lottery preferences and past return effects. We also document that this reference dependency of short-term reversal is stronger among stocks with low institutional ownership and during the low liquidity period.

Monotone Split and Conquer for Anomaly Detection in IoT Sensory Data

Anomaly detection is essential to guarantee the correctness of sensory data collected from Internet of Things. The latest detection approaches only operate under one of the two general forms of short-term or long-term anomaly. In this article, we propose monotone split and conquer (MSC) scheme to tackle both anomaly forms. The proposed scheme exploits the spatial–temporal correlation between neighboring sensors to detect abnormal sensory data. MSC splits the collected data into monotonic subtrends in the training phase to establish the trend-based normal profiles for the online detection phase. To eradicate the overfitting phenomenon, we further develop a general formulation to estimate the square prediction error (SPE) control limit. Both monotone split and general formulation contribute to the advancement of MSC in terms of accuracy (ACC) and false positive rate (FPR) in the online detection phase. To evaluate the performance of MSC, we design a general anomaly model to generate artificial short-term and long-term anomalies. Numerical experiments with the Intel Berkeley Research Lab (IBRL) data set demonstrate that MSC obtains about 8% higher ACC and 5% lower FPR on average when compared to existing schemes. Remarkably, MSC requires only a few observations for anomaly detection as it is applicable to real-time systems.

Short-term price-performance analysis of initial public offerings: an application on health industry in NYSE

Purpose - The purpose of this study is to investigate short-term underpricing anomaly of IPOs in health industry firms in USA. This study tried to test short-term underpricing anomaly that suggests investors may able to get abnormal returns by purchasing stocks at issuance date and selling them after holding for short time period. Methodology – Analysis period is taken into consideration as first 7 days after the issuance. To conduct analysis in the study, a sample, which includes 12 listed firms, is built. Stock returns are calculated from issuance date until 7th day. First raw returns are calculated based on price movements of each IPO and then abnormal returns are calculated by comparing them to NYSE index return. In order to get smoother series to reflect normal distribution features, compound abnormal returns are calculated. Findings – Raw returns are positive but significant only on 5th day after issuance. Abnormal returns except for 2nd and 3rd day are positive but statistically significant only 5th day after issuance. Compound abnormal returns are positive except for 3rd day but similarly it is statistically significant on 5th day after issuance. Based on test results, an investor who purchased stocks at the issuance and hold them until 5th day would get higher return (abnormal return) by %0,71 and higher compound return (compound abnormal return) by %1,23 than market average. Conclusion – According to results of t-test, it can claimed that underpricing anomaly can be confirmed for the firms are traded in health industry in NYSE.

Short term underpricing anomaly and its determinant factors on seasoned equity offerings: A research on the stocks traded on the Borsa Istanbul (BIST)

Purpose - The main objective of this study is to analyze the short-term price performance of the stocks issued by the 58 companies conducted 79 seasoned equity offerings (seos) during the 2010-2015 period in Borsa Istanbul and find out its determinant factors on the short-term price anomalies. Methodology – Raw and abnormal returns were calculated then t statistics were obtained for each type of returns. All returns were compared to market average and peer groups returns. The hypotheses were tested via the comparison t statistics and t values. Regression analysis was used to determine what kind of determinants affect long-term price performance. To find out underperformance anomaly’s determinants regression analysis was used through Panel Dynamic OLS (PDOLS) method. The analysis was also conducted based on year and sector separately. Findings- Short-term price performance of firms that performed seos during the 2010-2015 period are the function of two dimension consist of time duration and industry because price performance of the stocks can vary depending on these factors. Conclusion- According to the t-test results, the short-term underpricing anomaly cannot be fully confirmed in Borsa Istanbul during the analysis period. It has been confirmed statistically only in 2011 and 2015 years and in the stocks of the industrial sector. In other words, it is possible for investors to obtain higher returns than market average in the short term if they purchase shares from the seos performed in 2011 and 2015 carried out by companies in the industry sector. Determinants that considered as independent variables in study include; Stock Price, Number of Public Offerings, Company Size, Public Offering Method, Transaction Volume, Difference, Leverage Ratio, Capital Increase Rate, M / B ratio and Volatility. Based on panel regression analysis, leverage ratio change, capital increase rate and public placement have positive effect on share price performance while other variables such as M / B ratio and private placement have a negative impact.

OGLE-2017-BLG-0482Lb: A Microlensing Super-Earth Orbiting a Low-mass Host Star

Abstract We report the discovery of a planetary system in which a super-Earth orbits a late M-dwarf host. The planetary system was found from the analysis of the microlensing event OGLE-2017-BLG-0482, wherein the planet signal appears as a short-term anomaly to the smooth lensing light curve produced by the host. Despite its weak signal and short duration, the planetary signal was firmly detected from the dense and continuous coverage by three microlensing surveys. We find a planet/host mass ratio of q ∼ 1.4 × 10−4. We measure the microlens parallax from the long-term deviation in the observed lensing light curve, but the angular Einstein radius cannot be measured because the source trajectory did not cross the planet-induced caustic. Using the measured event timescale and the microlens parallax, we find that the masses of the planet and the host are and , respectively, and the projected separation between them is au. The estimated distance to the lens is kpc. The discovery of the planetary system demonstrates that microlensing provides an important method to detect low-mass planets orbiting low-mass stars.

Observational Evidence for Desert Amplification Using Multiple Satellite Datasets

Desert amplification identified in recent studies has large uncertainties due to data paucity over remote deserts. Here we present observational evidence using multiple satellite-derived datasets that desert amplification is a real large-scale pattern of warming mode in near surface and low-tropospheric temperatures. Trend analyses of three long-term temperature products consistently confirm that near-surface warming is generally strongest over the driest climate regions and this spatial pattern of warming maximizes near the surface, gradually decays with height, and disappears in the upper troposphere. Short-term anomaly analyses show a strong spatial and temporal coupling of changes in temperatures, water vapor and downward longwave radiation (DLR), indicating that the large increase in DLR drives primarily near surface warming and is tightly associated with increasing water vapor over deserts. Atmospheric soundings of temperature and water vapor anomalies support the results of the long-term temperature trend analysis and suggest that desert amplification is due to comparable warming and moistening effects of the troposphere. Likely, desert amplification results from the strongest water vapor feedbacks near the surface over the driest deserts, where the air is very sensitive to changes in water vapor and thus efficient in enhancing the longwave greenhouse effect in a warming climate.

Events, episodes, and phases: Signal from noise in flood-sediment archives

Abstract Major floods have increased in frequency in many parts of the world, and this is often attributed to anthropogenic climate change. Because of the short length of most gauged records (∼50 yr), it is unclear whether these events represent a short-term anomaly or a shift to a prolonged flood-rich period. In this paper, we use event-scale paleoflood records from upland and lowland floodplains to demonstrate the relationship between individual flood events, clusters of events in multiyear episodes, and multidecadal- to centennial-scale flood-rich phases. Catchment- and regional-scale data show that individual events and episodes generally fall within extended flood-rich phases controlled by climate. Furthermore, contrary to recent suggestions that environmental signals may be rendered incomplete in fluvial systems by autogenic processes, from a multidecadal (and longer) perspective it is clear that floodplain environments can register and preserve a useful multiscale hydromorphic signal of climate change.

OGLE-2013-BLG-0102LA,B: MICROLENSING BINARY WITH COMPONENTS AT STAR/BROWN DWARF AND BROWN DWARF/PLANET BOUNDARIES

We present the analysis of the gravitational microlensing event OGLE-2013-BLG-0102. The light curve of the event is characterized by a strong short-term anomaly superposed on a smoothly varying lensing curve with a moderate magnification $A_{\rm max}\sim 1.5$. It is found that the event was produced by a binary lens with a mass ratio between the components of $q = 0.13$ and the anomaly was caused by the passage of the source trajectory over a caustic located away from the barycenter of the binary. From the analysis of the effects on the light curve due to the finite size of the source and the parallactic motion of the Earth, the physical parameters of the lens system are determined. The measured masses of the lens components are $M_{1} = 0.096 \pm 0.013~M_{\odot}$ and $M_{2} = 0.012 \pm 0.002~M_{\odot}$, which correspond to near the hydrogen-burning and deuterium-burning mass limits, respectively. The distance to the lens is $3.04 \pm 0.31~{\rm kpc}$ and the projected separation between the lens components is $0.80 \pm 0.08~{\rm AU}$.

Physical and geochemical controls on sedimentation along an ancient continental margin: The deep-marine Old Fort Point Formation (Ediacaran), southern Canadian Cordillera

Abstract The approximately 608 Ma Old Fort Point Formation (OFP) is a unique, mixed siliciclastic and carbonate stratigraphic marker horizon exposed locally over an area of about 35 000 km2 within the Neoproterozoic Windermere Supergroup (WSG) of the southern Canadian Cordillera. Paleogeographically, these strata were deposited by a variety of deep-marine processes in slope to basin-floor settings along the continental margin of Laurentia (ancestral North America). The OFP ranges from approximately 60 to 450 m thick and comprises three informal lithostratigraphic members, which stratigraphically upward are the Temple Lake (TLM), Geikie Siding (GSM) and Whitehorn Mountain (WMM) members. The TLM and GSM are generally uniform in thickness and lithofacies and are interpreted to reflect basin-wide, synchronous deposition. The TLM is characteristically composed of variably coloured fine-grained rocks that stratigraphically-upward grade from siltstone to rhythmically bedded limestone-siltstone couplets. These fine-grained strata represent deposition during a major, post-glacial eustatic rise that essentially terminated the supply of coarse-grained siliciclastic sediment into the deep-water part of the Windermere basin. These strata are then gradationally overlain, although over an interval only <0.5–2 m thick, by strata of the GSM that stratigraphically-upward become progressively more organic-rich. The GSM is interpreted to have accumulated during terminal transgressive and highstand conditions, likely in anoxic bottom-water below a postulated pycnocline. The youngest member of the OFP is the WMM. The base of the WMM is almost always sharp and locally marked by scours more than 100 m deep. This surface is interpreted to be the result of an abrupt fall of relative sea level related to regional tectonic uplift, which in turn caused widespread mass wasting on the slope, and locally the formation of deeply incised submarine canyons. Sediment that accumulated in the canyons and more distally on the basin floor during the ensuing lowstand and early transgression was composed of remobilized slope sediment mixed with texturally and mineralogically immature clastic sediment derived directly from the hinterland. As transgression proceeded, the shelf eventually became flooded and shut-off the hinterland sediment supply. At the same time (late transgression and/or highstand), however, new, more landward canyons formed, or existing canyon heads eroded headward and reactivated the slope-basin floor transport system. This time, however, sediment was made up of a mixture of texturally and mineralogically mature palimpsest siliciclastic and carbonate shelf sediments. Notwithstanding its unique lithological and geochemical characteristics, strata of the OFP are underlain and overlain by a thick monotonous succession of mostly siliciclastic deep-marine sandstones and mudstones, suggesting that deposition of the OFP represented only a short-term anomaly superimposed on a much longer-term history of physical and geochemical stability throughout the Neoproterozoic deep-water Windermere basin.

Evolutionary patterns and palaeobiogeography of Pliensbachian and Toarcian (Early Jurassic) Radiolaria

Recent studies on the global distribution of Pliensbachian and Toarcian polycystine radiolarians allowed us to examine faunal turnovers and the biogeography through this critical time interval around a major ecologic and biotic crisis. The analysis is based on the distribution of 167 species belonging to 69 genera. Significant variations in the ratio between the number of originating and extinct species have been recognized. During the early Early Pliensbachian FADs greatly exceeded LADs and the maximum diversity was reached in the late Early Pliensbachian. The trend then reversed with the number of LADs exceeding FADs throughout the Late Pliensbachian and Early Toarcian (extinction interval). Recovery started in the Middle and Late Toarcian, when the number of FADs again surpassed the number of LADs.Three differing evolutionary patterns are observed amongst radiolarian genera through the studied time interval. The largest group diversified rapidly in the Early Pliensbachian and experienced higher extinction rates in the Late Pliensbachian and Early Toarcian; a second group exhibited no major changes; and a third group of mainly spongy spumellarians was successful during the extinction interval. The overall trend of radiolarian diversity is in a fairly good agreement with that of other marine faunas (ammonites and also benthos), but shows an inverse correlation with diversity trends of phytoplankton.Correlation with concomitant environmental changes indicates that radiolarian radiation/extinction rates were not consistently linked with temperature fluctuations or sea-level changes. It is also evident that the diversity decrease started well before the Early Toarcian negative δ13C peak and the Oceanic Anoxic Event (OAE). The extinction interval corresponds well to the duration of a short-term anomaly in the strontium-isotope record, including the rapid decrease of 87Sr/86Sr values in the Late Pliensbachian as well as the rapid increase in the Early Toarcian. This coincidence supports the hypothesis that the predominance of extinctions over originations was caused by a series of climate and environmental changes related to intensified magmatic activity.Some distinct biogeographic differences have been observed. Generic differences are most strongly displayed by the presence or absence of a particular genus or by changes in abundance while species differences range from greater variability to having completely different species in separate palaeolatitudinal realms. Two groups of genera are distinguished: those that are common to abundant in the Tethys (low latitudes) and rare to absent in mid to high latitudes, and those common to abundant in mid to high latitudes and rare to absent in the Tethys.

The episodic and abrupt geochemical changes at La Fossa fumaroles (Vulcano Island, Italy) and related constraints on the dynamics, structure, and compositions of the magmatic system

Herein we report on the chemical and isotopic (C, H, O, and He) compositions of the fluids from La Fossa crater fumaroles of Vulcano from 1999 to 2010. Consistent with records obtained since the end of the 1980s, our data show that the geochemical features of the fumarole system have experienced several episodes of remarkable change, each lasting no more than a few months. Typical signatures of these short-term anomalies are large increments in CO2, N2, and He concentrations, coupled to increased 13C/12C isotopic ratios, but their meaning remains widely debated. Within a model of fumarolic fluids based on mixing between hydrothermal and magmatic endmembers, we have developed a novel approach to constrain chemical (He/CO2 and N2/He) and isotopic (13C/12C, D/H, and 3He/4He) ratios of the magmatic endmember during the short-term anomalies. Although much of the geochemical variability in fumaroles results from changes in mixing proportions, the magmatic fluid unquestionably shows significant variations in time. The magmatic He/CO2, N2/He, 13C/12C, and 3He/4He values throughout 1988–1996 differed from those feeding the anomaly at the end of 2004. Early clues of the new magmatic fluid appeared in 1998–1999, far from any short-term anomaly, whereas new and old magmatic fluids coexisted after 2004. We quantitatively prove that the detected geochemical changes are consistent with the degassing path of a magma having a latitic composition, and suggest the presence of two magma ponding levels at slightly different pressures, where bubble–melt decoupling can occur. The different He-isotope compositions at these levels suggest low hydraulic connectivity typical of a complex reservoir with dike and sill structures. In this framework, the short-term geochemical anomalies are probably due to gas accumulation at the top of magma bodies followed by massive escape, or activation of new degassing levels in the reservoir, for which the stress field almost certainly plays a key role. Such a scenario explains the observed increases in both fumarole output and shallow high-frequency seismicity (due to increased pore pressure) during the anomalies, while being consistent with the concomitant absence of any deep seismicity or ground deformation, eventually related to magma movement.

The Variation of Waveform and Analysis of Composition for the Geoelectrical Field before Moderate and Strong Earthquakes in Qinghai‐Tibetan Plateau Regions

AbstractSite‐selective phenomenon exists in the normal waveforms of the geoelectrical fields of Qinghai‐Tibetan Plateau and its adjacent areas: rock structure of the sites, cracks and fissure water, tectonic activity and other factors affect the normal waveforms of the geoelectrical field; a large lake will contribute to the occurrence of TGF‐A waveforms nearby, TGF‐B waveforms will mostly occur in the areas where there are thick Quaternary sediments, and high water content and good water permeability of rocks, while the geoelectrical fields with no diurnal variations are prone to appear in the bedrock mountains where there are intense tectonic activities. Before moderate or strong earthquakes in the region, short‐term and impending anomaly of the geoelectrical field has a cluster phenomenon, in which there is a temporal synchronization or a few days' difference, while spatially it can be distributed near several faults in the region, manifested as a discrete phenomenon. This phenomenon of temporal clustering and spatial scattering is the short‐term and impending precursor characteristics of the geoelectrical field in the region. The Σ – Δ summation method is introduced to analyze the usual stability of spontaneous field through the observational data of the geoelectrical field, which indicate that before a moderate or strong earthquake, background value jumps of part of geoelectrical fields are a transformation phenomenon of spontaneous field; the concept and calculation method of TA, which is the sum of the first 10 order tidal harmonic amplitudes divided by the sum of the first 100 order harmonic amplitudes, are established to show quantitatively that the tidal effect of waveforms of TGF‐A, TGF‐B and non‐diurnal variation is successively reduced; the first order difference method of ΔE is adopted to analyze the higher frequency electromagnetic components in the minute order geoelectrical field monitoring data, usually the high‐frequency jumps show a certain degree of randomness and limitedness. By using three different methods of analysis, the features of spontaneous field, the telluric field and high‐frequency electromagnetic components are analyzed from the composition of the geoelectrical field, which provides a theoretical and methodological basis for the physical analysis of the geoelectrical field.

Satellite detection of thermal precursors of Yamnotri, Ravar and Dalbandin earthquakes

Prior to the occurrence of an earthquake, the region undergoes intensive physiochemical changes. Such changes trigger degassing charge generation leading to positive change in the thermal regime and consequently creation of an earthquake preparation zone. These changes in thermal regime can be detected by the thermal sensors onboard various polar orbiting satellites. Recent researches have demonstrated that thermal infrared sensors onboard satellites (e.g., NOAA-AVHRR and Terra/Aqua-MODIS) can detect temporal transient thermal infrared anomalies prior to an earthquake. The paper presents satellite-based thermal observations associated with Yamnotri (July 22, 2007, India), Ravar (October 14, 2004, Iran) and Dalbandin (January 19, 2011, Pakistan) earthquakes. In the case of Yamnotri earthquake, the region attained around 5–8°C higher than the normal temperature on July 21, 2007 in the area, just 1 day before the earthquake. Whereas, in the case of Ravar earthquake, the region has shown 5–7°C higher temperature on October 06, 2004 about 6 days before the occurrence of the main earthquake event. Dalbandin earthquake showed a maxima on January 17, 2011, just 2 days before the main shock with the raised temperature of around 8–10°C. Another common observation in all these earthquakes is the disappearance of short-term transient thermal anomaly just before the main shock.

The Short-Term Corporate Bond Anomaly

This paper finds that common risk factors significantly underestimate the returns on corporate bonds with a short maturity. A substantial portion of short-term corporate bond returns is independent of risk premiums associated with market risk, term and default risk, yield curve dynamics, liquidity risk and premiums associated with macro-economic variables. Comparable evidence of the short-term corporate bond anomaly also shows up in portfolios of corporate bond mutual funds, indicating that the anomaly withstands important practical issues, such as short-selling restrictions, transaction costs, and illiquidity.

Effects of Heterogeneity in Rock Samples on Spatial and Temporal Distribution of Acoustic Emission and Their Significance for Seismology

AbstractBased on a set of experimental results, we discuss the effects of heterogeneity (pre‐existing microcracks and macrostructures) in rock samples on spatial and temporal distribution of acoustic emission (AE). The comparative analysis indicates that the existence of pre‐existing microcracks makes AE occurrence rate rapidly increase prior to the fracture nucleation and b‐values show a short‐term anomaly, i.e. fluctuations of b‐value on a decreasing background, which increases the predictability of the fracturing time. The effects of pre‐existing macrostructures (joint, bedding plane) on AE occurrence rates and b‐values are the same as that of microcracks. AE spatial distribution is controlled by the pre‐existing macrostructures and the macrostructure clustered by AE events usually controls the coming final fracture. This means that the existence of macrostructures makes prediction of the time and location of the final fracture become possible.