Precursory Signals Research Articles

Contribution of Northeastern Asian stratospheric warming to subseasonal prediction of the early winter haze pollution in Sichuan Basin, China

Predicting the interannual (IA) variability of the early winter haze pollution (HP) in Sichuan Basin (SCB) and analyzing the contribution of the complex terrain are of great significance and challenge as well. For one thing, this study finds that the second mode of early winter IA variations of the HP in Central Eastern China (CEC) is dominated by the pollutant pattern of SCB, characterized by an extreme value center located over SCB. For another, the mode accounts for 15.1% of the total variance and well represents the IA variability of the areal mean HP in SCB. Furthermore, the anomalous circulations conducive to the severe HP in SCB consist of the strengthened (weakened) north (south) branch of Tibetan Plateau (TP) bypassing westerlies at 700 hPa, enhanced descents over SCB, and a strong inversion layer at 750 hPa, suppressing the precipitation and the development of the planetary boundary layer (PBL) in SCB. As a result, dispersion and wet deposition conditions are poor, favorable for the occurrence of the HP in SCB.Observed evidences show that the regional warming in the upper stratosphere over Northeastern Asia in November can be a possible subseasonal precursory signal for the SCB mode. Above all, the warming at upper stratosphere will propagate downward and arrive at the lower stratosphere in 3–4 weeks. Followed by the southward and downward propagation through the longitudinal tilted isothermal surface, the warming arrives at the tropospheric mid-low latitudes in 2–3 weeks, leading to anomalous warming and descents over TP and SCB. Consequently, SCB sees the aforementioned three-dimensional anomalous circulations. For this reason, a physical-empirical subseasonal prediction model for the IA variability of the early winter HP in SCB is established in terms of the regional stratospheric temperature in November. Apparently, the hindcast shows a promising prediction skill.

The Transition Zone Beneath West Argentina‐Central Chile Using P‐to‐S Converted Waves

AbstractWe investigate the mantle transition zone beneath the Chile‐Argentina flat subduction region by means of P‐to‐S conversions at mantle discontinuities from teleseismic events recorded at 103 seismic stations. From the analysis of receiver functions, we obtain clear converted phases from the 410 and 660 discontinuities, and we identify a robust precursory signal to P660s, of negative amplitude, that we name P590s. We observe little frequency dependence in the amplitude of the P410s converted phase, while the P660s is less visible toward higher frequencies. The 410 is on average deeper than 410 km by 10 ± 1 km in the higher‐frequency bands, and it is relatively sharp, being consistent with a 10% velocity jump over less than 20 km. The observed 660 depth varies with frequency; it is deeper by up to 18 ± 2 km for lower frequencies and close to reference at higher frequencies, being consistent with a 13% broad velocity gradient over 30–40 km, probably caused by a composite of multiple phase transitions. The transition zone thickness is controlled by the frequency‐dependent depth variability of the 660. Our findings of relative depth, width, and velocity jump of the detected discontinuities, combined with tomographic images of the mantle transition zone, cannot be explained by thermal variations alone. Compositional constraints from mineral physics show that a near pyrolitic mantle is consistent with the ratio of the estimated velocity jumps. However, the negative P590s phase in this region could be signal from the velocity reduction due to basalt accumulation at the base of the transition zone.

An earthquake prediction model based on precursor window detection

The research of the earthquake precursor signal anomaly is one of the main research directions of short-term and imminent earthquake prediction. An earthquake prediction method based on time precursory window is proposed in this paper, which is based on the low-frequency electromagnetic signals collected by AETA. Firstly, the prediction model of historical low-frequency electromagnetic signals is constructed by machine learning method. The model is used to detect whether the current time period is in the window of earthquake precursors. Furthermore, two algorithms based on single-site and group-site position prediction is proposed in this paper. The algorithm filters three or more stations within the effective distance range, and uses the probability of earthquake occurrence as the weight to locate the earthquake center, so as to predict the position of earthquake occurrence. Finally, the real data set is tested on the earthquake of Qingchuan County, Guangyuan City, Sichuan Province, on February 18, 2018. The experimental results show that the proposed model has a good prediction effect.

Assessment of Rn-222 continuous time series for the identification of anomalous changes during moderate earthquakes of the Garhwal Himalaya

Over years, soil radon (Rn-222) measurement was started at Multi-parametric Geophysical Observatory (MPGO), Ghuttu, Garhwal Himalaya to assess the earthquake precursory signatures. We carried out a statistical analysis to examine anomalous soil radon emanation during the occurrence of local earthquakes. Twenty earthquakes of moderate and bigger magnitude are occurred within 300 km from MPGO, Ghuttu during 2009–2017. Continuous time series highlight a high effect of rainfall precipitation on the soil radon emanation measured at 10 m depth. During monsoon period (June to September), high rain precipitation at the recording site cause a high variation in the radon emanation. In spite of our best efforts, it is difficult to isolate the complex behavior of heavy and abrupt occurrence of rain from the soil radon data. Preferably, the data of 11 events of the pre- and post-monsoon are evaluated to identify the seismic origin effect on soil radon. To examine these anomalous variations, statistical analysis of soil radon data is carried out by calculating mean (m), and then obtaining standard deviation (σ) from mean values. Changes in the soil radon concentration are treated anomalous for values exceeding one and two standard deviations (m±σ and m±2σ) from the mean value for the selected duration. Two nearby and the strongest events suggests pre-seismic variations which are related to the earthquake precursory signatures. The observed results are explained in the light of dilatancy- diffusion model.

New Opportunities to Study Earthquake Precursors

New Opportunities to Study Earthquake Precursors

Implementation of a multiple-fraction concatenation strategy in an online two-dimensional high-/low-pH reversed-phase/reversed-phase liquid chromatography platform for qualitative and quantitative shotgun proteomic analyses.

Multidimensional liquid chromatography is the mainstay separation technique used for shotgun proteomic analyses. The application of a multiple-fraction concatenation (MFC) strategy can result in a more disperse and consistent peptide elution profile across different fractions, when compared with a conventional strategy. Herein, we present the first automated online RP-RP platform implementing an MFC strategy to facilitate robust, unattended, routine proteomic analyses. The improved duty cycle utilization of the MFC strategy led to an increase of 9% in the separation space occupancy and increases of approximately 10% in the identification of both proteins and peptides. The peptides uniquely identified by the MFC strategy were significantly biased toward those of acidic nature, with increased precursor signals leading to improved MS/MS spectral quality and enhanced acidic peptide identification. These improvements in qualitative analysis using the MFC strategy were also extended to quantitative analysis. When the acquired proteome was quantified with a normalized spectral abundance factor, the additionally acquired acidic peptides were a critical factor leading to enhanced reproducibility of quantitation using the MFC strategy. With merits of superior qualitative and quantitative characteristics over the conventional strategy, the MFC strategy appears to be a highly amenable technique for enhancing the separation capacity for routine proteomic analyses.

Previous, Current, and Future Trends in Research into Earthquake Precursors in Geofluids

Hazard reduction policies include seismic hazard maps based on probabilistic evaluations and the evaluation of geophysical parameters continuously recorded by instrumental networks. Over the past 25 centuries, a large amount of information about earthquake precursory phenomena has been recorded by scholars, scientific institutions, and civil defense agencies. In particular, hydrogeologic measurements and geochemical analyses have been performed in geofluids in search of possible and reliable earthquake precursors. Controlled experimental areas have been set up to investigate physical and chemical mechanisms originating possible preseismic precursory signals. The main test sites for such research are located in China, Iceland, Japan, the Russian Federation, Taiwan, and the USA. The present state of the art about the most relevant scientific achievements has been described. Future research trends and possible development paths have been identified and allow for possible improvements in policies oriented to seismic hazard reduction by geofluid monitoring.

Potential impacts of the Southern Hemisphere polar vortices on central-eastern China haze pollution during boreal early winter

Understanding the spatial–temporal evolution of China haze pollution (HP) and identifying its precursory signals is of central importance. Based on observational data across central-eastern China (CEC) for the period of 1980–2015, this study finds that HP interannual variations in the CEC region during the most polluted season (December–January) are mainly dominated by a homogeneous pattern with maximum loading centers located over the Central China, Yangtze River Delta, and South China, which accounts for 42.3% of the total variances. The circulations conducive to such polluted mode feature barotropic high anomalies over central-eastern China. Correspondently, the related anomalous weather and circulation conditions with less precipitation, low-level dryer air, weaker surface wind speed, more descending movement, and more upstream transportation of aerosols at the northeast and southeast planks of the anomalous high, leading to the HP frequently occur in the CEC region, and vice versa. Observed evidences show that the combined effects of the Southern Hemisphere tropospheric and stratospheric polar vortices (SHPV) in August and September (AS), can exert profound effects on the HP dominant mode. Notable circulation anomalies associated with the combined effects of the SHPV, prevailing over the ocean off the south-west Western Australia, can induce sea surface temperature (SST) anomalies around the ocean off the south-west Western Australia. This anomalous SST pattern in AS can persist into the following early winter and impact the HP variations by modulating the Hadley cell and correspondently circulation anomalies over central-eastern China. Based on the preseason SHPV signal, we establish a physical-empirical seasonal prediction model to predict the HP dominant mode variations. The hindcast shows a promising prediction skill. Since the regional PV anomalies linked to the combined effects of the SHPV could be monitored in preceding autumn, the HP over the CEC in early winter can be forecasted in real-time by this empirical model.

Unexpected large eruptions from buoyant magma bodies within viscoelastic crust

Large volume effusive eruptions with relatively minor observed precursory signals are at odds with widely used models to interpret volcano deformation. Here we propose a new modelling framework that resolves this discrepancy by accounting for magma buoyancy, viscoelastic crustal properties, and sustained magma channels. At low magma accumulation rates, the stability of deep magma bodies is governed by the magma-host rock density contrast and the magma body thickness. During eruptions, inelastic processes including magma mush erosion and thermal effects, can form a sustained channel that supports magma flow, driven by the pressure difference between the magma body and surface vents. At failure onset, it may be difficult to forecast the final eruption volume; pressure in a magma body may drop well below the lithostatic load, create under-pressure and initiate a caldera collapse, despite only modest precursors.

Impact of atmospheric quasi-biweekly oscillation on the persistent heavy PM2.5 pollution over Beijing-Tianjin-Hebei region, China during winter

In recent years, persistent heavy PM2.5 pollution (PHP) events occurred frequently over the Beijing-Tianjin-Hebei (BTH) region in China, which posed a great threat to human life. This study investigates the evolution of PHP over the BTH region in China and its relation with atmospheric quasi-biweekly oscillation. A significant periodicity of 10–16 days of the PM2.5 concentration over the BTH region is observed in winters of 2013–2017, which notably contributes to the occurrence of PHP. A total of 12 PHP events are identified in the five winters. The life cycle of PM2.5 pollution containing those PHP events is divided into eight phases according to the quasi-biweekly variation of PM2.5 pollution over the BTH region. The phase composites of circulation fields show that the atmospheric quasi-biweekly oscillation provides favorable conditions for the persistence of air pollution over the BTH region in winter. During the PHP events, the quasi-biweekly southerly anomalies prevail persistently over eastern China. The East Asian winter monsoon is weakened and more moisture is transported to the BTH region continuously. The anomalous warming in the lower troposphere indicates a stable stratification on a quasi-biweekly time scale. Moreover, in the mid-troposphere, the variation of East Asian trough's intensity is significantly correlated with PHP over the BTH region. It is suggested that the quasi-biweekly oscillation of East Asian trough can be traced back to a precursor signal over northwestern Eurasia about 11 days earlier, through a southeastward wave train propagation. Thus, the meteorological conditions conducive to PHP over the BTH region can be predicted on the quasi-biweekly time scale.

Dynamic Diagnosis of Stratospheric Sudden Warming Event in the Boreal Winter of 2018 and Its Possible Impact on Weather over North America

In the winter of 2018, a major stratospheric sudden warming (SSW) event occurred in the Northern Hemisphere. This study performs a dynamic diagnosis on this 2018 SSW event and analyzes its possible impact on the weather over North America. The result shows that the ridge over Alaska in the mid-troposphere and the trough over the northeastern North America are the prominent tropospheric precursory signals before the occurrence of this SSW event. The signals appear 10 days before the SSW, which greatly enhances the propagation of the planetary wavenumber 2 from the troposphere to the extratropical stratosphere. The collapse process of stratospheric polar vortex indicates that this SSW is a typical vortex splitting event dominated by planetary wavenumber 2. Additionally, after the SSW onset, no reflection of the stratosphere on the tropospheric planetary waves is observed. Thus, this event can also be classified as an absorbing-type SSW event. A noticeable cold wave occurs in the northwestern North America within 10 days after the 2018 SSW. This cold wave is probably associated with the SSW-related west–east dipole, namely a ridge over Alaska and a trough over the northeastern North America in the mid-troposphere that lasted up to 10 days after the onset date. The composite analysis of the other seven SSW events with an emergence of similar mid-tropospheric circulation pattern after SSW onset date yields coincident 2-meter temperature anomalies in the northwestern North America, which confirms the above conclusion to some extent.

Pre-Event Deformation and Failure Mechanism Analysis of the Pusa Landslide, China with Multi-Sensor SAR Imagery

The Pusa landslide, in Guizhou, China, occurred on 28 August 2017, caused 26 deaths with 9 missing. However, few studies about the pre-event surface deformation are provided because of the complex landslide formation and failure mechanism. To retrieve the precursory signal of this landslide, we recovered pre-event deformation with multi-sensor synthetic aperture radar (SAR) imagery. First, we delineated the boundary and source area of the Pusa landslide based on the coherence and SAR intensity maps. Second, we detected the line-of-sight (LOS) deformation rate and time series before the Pusa landslide with ALOS/PALSAR-2 and Sentinel-1A/B SAR imagery data, where we found that the onset of the deformation is four months before landslide event. Finally, we conceptualized the failure mechanism of the Pusa landslide as the joint effects of rainfall and mining activity. This research provides new insights into the failure mechanism and early warning of rock avalanches.

Seismic characterization of a clay-block rupture in Harmalière landslide, French Western Alps

SUMMARYIn late June 2016, the Harmalière clayey landslide (located 30 km south of the city of Grenoble, French Alps) was dramatically reactivated at the headscarp after a 35-yr-long period of continuous but limited activity. The total involved volume, which moved as sliding blocks of various sizes, was estimated to be about 2 × 10 6 m3. Two seismometers were installed at the rear of the main headscarp in August 2016, on both sides of a developing fracture delineating a block with a volume of a few hundred cubic metres. For 4 months, they continuously recorded seismic ambient vibrations and microearthquakes until the block broke. Five seismic parameters were derived from the monitoring: the cumulative number of microearthquakes (CNe), the seismic energy (SE), the block resonance frequency (fB), the relative variation in Rayleigh wave velocity (dV/V) deduced from noise cross-correlations between the two sensors and the associated correlation coefficient (CC). All parameters showed a significant precursory signal before the rupture, but at very different times, which indicates the complexity of the rupture mechanism in this clay material.

Impacts of climate anomalies on the interannual and interdecadal variability of autumn and winter haze in North China: A review

AbstractFrom the perspectives of remote sensing and climatic factors like surface meteorological parameters, large‐scale atmospheric circulations, and external forcing factors (EFFs), the authors synthesize and review spatiotemporal variations of PM2.5 over North China and how climate anomalies affect autumn and winter haze variability in North China according to recent studies. This review focuses on both interannual and interdecadal timescales. It is shown that circulations play an important role in influencing haze variability. Atmospheric circulations, which would be modulated by EFFs like sea surface temperature, sea ice, and snowpack, can affect the climate variability in haze over North China via modulation of surface‐layer parameters that are closely connected with the haze phenomenon. Therefore, EFFs are deemed significant factors impacting the climate variability of haze over North China, serving as paramount precursory signals for haze prediction. Furthermore, this paper suggests potential future research directions for haze variability studies in North China on the basis of summarizing and concluding the associated processes/mechanisms on how climatic factors affect haze variability, which could provide reference for treating and forecasting in situ hazy conditions.

The loess landslide on 15 march 2019 in Shanxi Province, China

On 15 March 2019, a fatal deep-seated landslide occurred at the village of Zaoling in Xiangning County of Shanxi Province, China. Extending to an area of about 120 m by 85 m, with an estimated displaced mass volume of 72,000 m3, the landslide left 20 people dead, 13 injured, and 8 buildings destroyed. There were no precursory signals prior to the event, and usual triggering mechanisms for a landslide were absent. Investigation conducted immediately after the incident revealed that the landslide was initiated in a 1.0 to 1.5-m thick-softened layer located at 40 m depth along the contact between the loess and interbedded paleosol layer. This softened layer was highly saturated due to the perched water on top of the relatively impervious paleosol layer and became a critical weak zone since the shear strength of loess is very sensitive to water content. We suggest that the perched water originated from extensive long-term unsaturated seepage of rainwater and local rapid percolation along preferential channels such as sinkholes and root network. The Zaoling landslide confirms that unlike most landslides in non-loess areas, loess landslides can occur without identifiable triggering events. They can result from gradual build up of instability due to slow (in the span of hundred years) accumulation of deep soil water. Based on the lessons learned from this landslide event, suggestions are given for the planning of urban and rural development in loess areas. Due to the fact that the process leading to the development of such a landslide is largely concealed, further research should be aimed at gaining a more thorough understanding of the mechanism of this landslide type.

Weibull distribution analysis of precursory time due apparent resistivity anomaly prior to earthquakes in the vicinity of multi-parametric geophysical observatory, Tezpur, India

The apparent resistivity imaging at multiparametric geophysical observatory (MPGO), Ouguri Hills, Tezpur was carried out since 31st August, 2016 for fixed interval time of 3 days to investigate precursory signature prior to earthquake events. Anomalies in apparent resistivity prior to earthquake events are observed. The anomalies are not influenced by the rainfall activity in the region during the investigation period. We adopt Weibull distribution technique with observed apparent resistivity data to look for and revalidate the observations. The Weibull parameters, i.e. K and m are estimated to be 0.26 and 1.04, respectively. No precise relation between magnitude and earthquake precursory time is found. Simultaneously, an attempt has been made to establish a relation between the earthquake magnitude (M) and precursory time (T) and a relation between the earthquake precursory time (T) and distance of the earthquake (Δ) from the observation point. Weibull probability distribution indicate the probability of an earthquake occurrence exceeds the measure up to 80% (9 days) after the precursory signal is observed. A comparison of probability analysis ascertains a mean precursory time and its standard deviation.

Research on Anisotropic Characteristics of Rock and Intelligent Recognition of Precursory Signal

In order to study the change in anisotropic characteristics of rock materials during the uniaxial compression process, an advanced ultrasonic experimental device and loading device are used to establish an experimental system for measuring ultrasonic waveform in three orthogonal directions in real‐time. The experimental results show that there exists pronounced difference between ultrasonic receiving waveform in axial and radial directions. Based on the multifractal theory, multifractal spectrums of receiving waveform are calculated, and multifractal parameters (Δα and Δf) are further analyzed. The multifractal spectrum in the radial direction gradually becomes smaller, but the multifractal spectrum in the axial direction presents an “increase‐decrease” trend. During the entire uniaxial compression process, the anisotropic characteristics of the rock sample show an “enlarge‐reduce” trend, which is caused by the development and growth of microcracks. Furthermore, a quantitative relationship between multifractal parameter Δα and stress σ is proposed. It indicates that the parameters Δα and σ satisfy the power function. On this basis, a method is proposed that ultrasonic waveform precursor characteristics are recognized automatically using the backpropagation (BP) neural network to monitor the damage state of the rock sample. The application results show that this method can provide an early warning signal more than 100 seconds before the rock sample buckling failure. This research can provide a useful reference for studying the anisotropic characteristics of the rock sample during the uniaxial compression process. The proposed method in this paper has essential meaning for monitoring and early warning of rock stability.

On the Differences Between the South Pacific Meridional and Quadrupole Modes

AbstractThe South Pacific quadrupole (SPQ) and South Pacific meridional mode (SPMM) are the dominant modes of South Pacific sea surface temperature (SST) variability. Both SST modes have been found to affect the occurrence of El Niño‐Southern Oscillation (ENSO) events. In this study, the authors examine the differences between the SPQ and SPMM in terms of their spatial structure, temporal variations, and impacts on ENSO using observational and Coupled Model Intercomparison Project Phase 5 (CMIP5) model data. As a local SST mode defined in the subtropical southeast Pacific, the SPMM has large‐amplitude SST anomalies (SSTAs) mainly confined in the southeast Pacific. In contrast, as a basin‐scale SST mode defined in the South Pacific basin, the SPQ has large‐amplitude SSTAs over the southeast Pacific as well as over the southwest Pacific and high‐latitude South Pacific. In addition, the SPQ has its temporal variability independent of the SPMM, and the occurrence of strong SPQ events is not always simultaneous with strong SPMM events. The SPQ is more closely linked than the SPMM to ENSO, possibly because the SPQ includes an additional component of SSTAs in the southwest Pacific and high‐latitude South Pacific. These findings suggest that compared with the SPMM, the SPQ may act as an improved precursor signal for ENSO events. The results have implications for understanding the respective roles of SSTAs over different regions of the South Pacific in influencing ENSO.

Precursory and coseismic groundwater temperature perturbation: An example from Taiwan

We have conducted Taiwan’s first groundwater temperature earthquake precursory and coseismic signal study using totally 8-month time series of groundwater temperature from two monitoring wells in Eastern Taiwan. We applied Hilbert-Huang Transform (HHT) analysis to identify possible precursory signals, with periods ranging from one to ten minutes, and duration of tens of hours, that occurred one to three days before Mw > 4.7 earthquakes. These signals are not correlated with atmospheric and pumping processes. The precursors are sensitive to an earthquake within an epicentral distance that is about 20- to 25-time of the earthquake rupture length. With this limited dataset, we found the rates of false positives and false negatives are 16.7% and 28.6%, respectively. Exact physical processes that generate such signals are unclear and additional data are needed. But we propose that real-time groundwater temperature monitoring has potentials to become a low cost but beneficial way to complement other earthquake precursory projects for more robust short-term earthquake forecasting

Signals of Spring Thermal Contrast Related to the Interannual Variations in the Onset of the South China Sea Summer Monsoon

AbstractLand–sea thermal contrast is one of the key factors modulating the onset and strength of summer monsoons. This study investigates the precursory thermal-contrast signal of the onset of the South China Sea summer monsoon (SCSSM) and reveals that the land–sea thermal contrastDT(ToceanminusTlandat the surface) in March tracks the date of the monsoon onset very well. In an energy-balance framework, the monthly anomalies in this thermal contrast are decomposed into different components associated with the anomalies of various radiative and nonradiative dynamical processes over the South China Sea in early spring. It is found that the interannual variations ofDT, and thus the onset date of monsoon, are mainly tied to the anomalies in surface heat fluxes, ocean–land heat storage rate, and oceanic dynamical processes. The variation of ocean–land heat storage rate and ocean dynamics is the largest positive contributor to the change inDT. Specifically, an early SCSSM onset tends to be associated with an amplified “cold-land, warm-ocean” pattern that can be further attributed to increased soil moisture content in March, which enhances land surface cooling and weakens oceanic heat storage rate that benefits ocean surface warming. Furthermore, the variations ofDTand soil moisture content in March are positively related with the late-February precipitation over the Indochina Peninsula, which could therefore be regarded as a precursory signal for both the land–sea thermal contrast in March and the onset of the SCSSM.