Earthquake detection in the Jiangsu region, China using graphics-processing-unit-based Match & Locate and rapid earthquake association and location

Earthquake detection and location are essential in earthquake studies,which generally consists of two main classes:waveform-based and pick-based methods.To evaluate the ability of two different methods,a graphicsprocessing-unit-based Match&Locate(GPU-M&L)method and a rapid earthquake association and location(REAL)method are applied to continuous seismic data recorded by 24 digital seismic stations from Jiangsu Seismic Network during 2013 for comparison.GPU-M&L is one of waveform-based methods by waveform cross-correlations while REAL is one of pick-based method to associate arrivals of different seismic phases and locate events through counting the number of P and S picks and travel time residuals.Twenty-six templates are selected from the Jiangsu Seismic Network local catalog by using the GPU-M&L.The number of newly detected and located events is about 2.8 times more than those listed in the local catalog.We both utilize a deep-neural-network-based arrival-time picking method called PhaseNet and a shortterm/long-term average(STA/LTA)trigger algorithm for seismic phase detection and picking by applying the REAL.We then refine seismic locations using a least-squares location method(VELEST)and a high-precision relative location method(hypoDD).By applying STA/LTA and PhaseNet,1006 and 1893 events are associated and located,respectively.The newly detected events are mainly clustered and show steeply dipping fault planes.By analyzing the performance of these methods based on long-term continuous seismic data,the detected catalogs by the GPU-M&L and REAL show that the magnitudes of completeness are 1.4 and 0.8,respectively,which are smaller than 2.6 given by the local catalog.Although REAL provides improvement compared with GPU-M&L,REAL is highly dependent on phase detection and picking which is strongly affected by signal-noise ratio(SNR).Stations at southeast of the study region with low SNR may lead to few detections in the same area.

变权重连接P波和S波到时数据的微震震源Bayes定位方法及应用

微震震源定位是微震监测领域的一项关键性技术,传统的矿山微震定位方法采用基于P波或S波的走时射线追踪定位算法。然而,可用于微震事件定位的到时数据少,致使定位结果误差偏大。联合P波和S波到时的目标函数可取得更好的定位结果。已有研究面临着以下几个挑战:1)联合权重应该是一个由P波和S波到时数据质量决定的自由参数;2)对同一微震事件定位时,使用的全部到时数据中含有不良数据。为此,本文提出了一种变权重连接P波和S波到时数据的贝叶斯定位方法用于微震震源定位。为减少异常到时数据的影响,每次迭代随机选择80%的到时数据。本文使用2个理论事件和8个矿山爆破事件对所提出方法进行了测试。模拟结果表明,当分别在P波和S波的走时数据中添加2 ms和4 ms的高斯噪声时,采用本文方法的平均定位误差仅为9.96 m。应用结果表明,与单P波贝叶斯定位方法和单S波贝叶斯定位方法相比,采用本文方法的平均定位误差为31.97 m,定位精度分别提高了25.40%和60.78%。

Using the match-and-locate method to characterize foreshocks of the July 2019 M_(W)6.4 Ridgecrest,California earthquake

The July 2019 M_(W)6.4 Ridgecrest,California earthquake and its distinct foreshocks were well recorded by local and regional stations,providing a great opportunity to characterize its foreshocks and investigate the nucleation mechanisms of the mainshock.In this study,we utilized the match-and-locate(M&L)method to build a high-precision foreshock catalog for this M_(W)6.4 earthquake.Compared with the sequential location methods(matched-filter+cross-correlation-based hypoDD),our new catalog contains more events with higher location accuracy.The M_(W)6.4 mainshock was preceded by 40 foreshocks within~2 h(on July 4,2019 from 15:35:29 to 17:32:52,UTC).Their spatiotemporal distribution revealed a complex seismogenic structure consisting of multiple fault strands,which were connected as a throughgoing fault by later foreshocks and eventually accommodated the 2019 M_(W)6.4 mainshock.To better understand the nucleation mechanism,we determined the rupture dimension of the largest M_(L)4.0 foreshock by calculating its initial rupture and centroid points using the M&L method.By estimating Coulomb stress change we suggested that the majority of foreshocks following the M_(L)4.0 event and M_(W)6.4 mainshock occurred within regions of increasing Coulomb stress,indicating that they were triggered by stress transfer.The nucleation process before the M_(L)4.0 event remains unclear due to the insufficient sampling rate of waveforms and small magnitude of events.Thus,our study demonstrates that the M&L method has superior detection and location ability,showing potential for studies that require high-precision location(e.g.,earthquake nucleation).

P-wave Velocity Structure of Crustal and Upper Mantle beneath South China and its Tectonic Implications

The 3D P-wave velocity structure beneath the South China Block was determined by applying arrival times from 269 teleseismic events recorded by 240 seismic stations within the study region. Our tomographic results reveal the deep structural characteristics of major tectonic units and ore concentration areas. There are distinct high velocity anomalies beneath the ancient Yangtze and Cathaysia blocks, with the lithosphere of the Cathaysia Block being thinner than the Yangtze Block;the Jiangnan orogenic belt, located in the combined zone of two blocks, is a high and low velocity anomaly conversion zone;the famous metallogenic belts of Edongnan, the Youjiang Basin and the Cathaysia Block are obviously low velocity areas with different metallogenic mechanisms. The deep ore-forming material source in the Edongnan metallogenic belt is different from that of the Cathaysia Block. The low velocity anomaly under the Cathaysia Block related to mineralization results from the upwelling of mantle material, caused by the joint action of the Paleo-Tethys tectonic domain, the Paleo-Pacific tectonic domain and the Hainan mantle plume migration and erosion, which has been occurring from northeast to southwest since 80 Ma. The low-temperature mineralization mechanism of Youjiang Basin should be considered not only in terms of the influence of the Emeishan mantle plume in the west and the Paleo-Tethys tectonic domain in the south, but also in the context of the influence of the upwelling of asthenospheric material from the PaleoPacific tectonic domain in the east.

Near-surface structure from ambient-noise tomography and horizontal-to-vertical spectral ratio beneath the Nankou-Sunhe fault

Active faults pose a great threat to urban security.As the largest NW-trend active fault in Beijing area,the Nankou-Sunhe fault plays an important role in earthquake disaster and city construction.In this study,we collect continuous ambient noise data recorded by 43 temporary short-period seismograph between September 21th to October 12th 2019 to investigate the near-surface structure beneath the Nankou-Sunhe fault by using ambient noise tomography(ANT)and horizontal-to-vertical spectral ratio(HVSR)method.From ambient noise processing,fundamental-mode Rayleigh wave signals are clearly observed in the frequency band of 0.4-2.5 Hz.Then direct surface-wave inversion algorithm is applied to calculate the 3D shear-wave velocity model.Our results show that there is a sharp velocity contrast across the Nankou-Sunhe fault,with low velocities down to about 2 km on the hanging wall and high velocity on the footwall of the fault.According to the geological investigation,the low velocities are related to thicker sediments and Jurassic volcanic rock below which are the cap rock of the hydrothermal system.From the HVSR analysis,the HVSR curves of the sites near the fault shows double-peak,one less than 1 Hz and the other centered 7 Hz.After converting frequency to depth by the empirical equation,the results show that the thickness of sediments is thinned from southwest to northeast,which generally agrees well to field survey.Our results provide high-resolution near-surface structure for future study on disaster risk reduction and urban planning.

Metabolic activities of marine ammonia-oxidizing archaea orchestrated by quorum sensing

Ammonia-oxidizing archaea(AOA)play crucial roles in marine carbon and nitrogen cycles by fixing inorganic carbon and performing the initial step of nitrification.Evaluation of carbon and nitrogen metabolism popularly relies on functional genes such as amoA and accA.Increasing studies suggest that quorum sensing(QS)mainly studied in biofilms for bacteria may serve as a universal communication and regulatory mechanism among prokaryotes;however,this has yet to be demonstrated in marine planktonic archaea.To bridge this knowledge gap,we employed a combination of metabolic activity markers(amoA,accA,and grs)to elucidate the regulation of AOA-mediated nitrogen,carbon processes,and their interactions with the sur-rounding heterotrophic population.Through co-transcription investigations linking metabolic markers to potential key QS genes,we discovered that QS molecules could regulate AOA's carbon,nitrogen,and lipid metabolisms under different conditions.Interestingly,specific AOA ecotypes showed a preference for employing distinct QS systems and a distinct QS circuit involving a typical population.Overall,our data demonstrate that Qs orchestrates nitrogen and carbon metabolism,including the exchange of organic metabolites between AOA and surrounding heterotrophic bacteria,which has been pre-viously overlooked in marine AOA research.

Double-Frequency Microseisms on the Thick Unconsolidated Sediments in Eastern and Southeastern Coasts of United States: Sources and Applications on Seismic Site Effect Evaluation

This study presents a systematic analysis of double-frequency(DF) microseisms recorded on the unconsolidated sediments in the eastern and southeastern coasts of United States. For all recordings, the site effect parameters(predominant frequency(f_(0)), amplification factor and unconsolidated sediment thickness(UST)) are obtained by Nakamura method and the DF spectra are classified into five groups in terms of the DF peak patterns and the recording locations relative to the coastline. The frequencies and energy levels of the DF peaks in horizontal direction and the amplification factors are associated with the UST which is resulted from seismic site effect. By polarization analysis, the primary vibration directions of the DF peaks are identified and presented as great circles passing through the recording stations intersecting mainly along the continental slope. Correlation analyses of time histories of the DF energy and the ocean wave climate observed at buoys show that the low(<0.2 Hz) and high(>0.2 Hz) frequency DF microseisms are generated in the deep ocean and the continental shelf respectively. It is concluded that the continental slope plays a significant role in the generation of DF microseisms as it causes reflection of waves from the open ocean, initiating standing waves.

Locating the Source Regions of the Single and Double-Frequency Microseisms to Investigate the Source Effects on HVSR in Site Effect Analysis

Evaluating the seismic site effect by the ambient noise based horizontal-to-vertical spectral ratio(HVSR)method is strongly affected by the spatial and temporal variations of the ambient noise sources.Therefore,it is necessary to locate the source regions of ambient noise and investigate the relationships between the source energy and HVSR values at the predominant frequency(HVSRf_(0))of the site.The generation mechanisms of the single-and double-frequency microseisms(SFMs,0.05-0.085 Hz and DFMs,0.1-0.5 Hz)in ambient noise are better understood than the noise in other frequency bands and they are dominantly composed of fundamental Rayleigh(Rg)waves.With this advantage,the recordings of SFMs and DFMs at 30 stations in the east coast region of the United States are used to demonstrate a study on locating their source regions with reasonable certainty and constructing the functional relationship between the HVSRf_(0) and the source energy of SFMs and DFMs.The recordings are processed in four sub-frequency bands(Fs)of SF and DF bands and a polarization analysis is carried out to select the ellipsoids approximating the particle motions of Rg waves.Then the probability density functions of the back azimuths of the ellipsoids’semi-major axes are computed for each F and station,and are projected on the ocean to determine their possible source regions.These regions are further constrained by(1)the correlation coefficients between the SFMs and the WAVEWATCHⅢ(WWⅢ)hindcasts of ocean wave spectra in the SF band,or between the DFMs and the modeled DF energy on ocean surface in the selected time windows in the DF band,(2)the energy contribution defined by(i)the average WWⅢocean wave energy and the ocean bottom topographical gradient in the SF band,or(ii)the average modeled DF energy on ocean surface and a frequency and water depth dependent coefficient measuring the conversion efficiency of DF energy from water to solid earth in the DF band,and(3)the percentile retained energy of Rg waves in both the SF and DF bands.Results of source regions reveal that(1)the SFMs recorded in eastern US result from the interactions of low frequency(0.05-0.085 Hz)ocean waves with the continental slope and shelf of western North Atlantic Ocean;(2)the source regions for long-(0.1-0.2 Hz)period DFMs are located in the deep ocean close to the continental slope;and(3)the short-(0.2–0.5 Hz)period DFMs are generated in the continental shelf.Finally,the correlation analyses between the simulated source energy and the HVSRf_(0) values at the stations whose f_(0) s fall in DF band are carried out revealing significant source effect on thick sediments at low frequencies.

In situ identification of environmental microorganisms with Raman spectroscopy

Microorganisms in natural environments are crucial in maintaining the material and energy cycle and the ecological balance of the environment.However,it is challenging to delineate environmental microbes'actual metabolic pathways and intraspecific heterogeneity because most microorganisms cannot be cultivated.Raman spectroscopy is a culture-independent technique that can collect molecular vibration profiles from cells.It can reveal the physiological and biochemical information at the single-cell level rapidly and non-destructively in situ.The first part of this review introduces the principles,advantages,progress,and analytical methods of Raman spectroscopy applied in environmental microbiology.The second part summarizes the applications of Raman spectroscopy combined with stable isotope probing(SIP),fluorescence in situ hybridization(FISH),Raman-activated cell sorting and genomic sequencing,and machine learning in microbiological studies.Finally,this review discusses expectations of Raman spectroscopy and future advances to be made in identifying microorganisms,especially for uncultured microorganisms.

Lipidomics in archaeal membrane adaptation to environmental stresses and growth conditions:A review of culture-based physiological studies

Membrane lipids are thought to be a crucial part of the homeoviscous adaptation of archaea to extreme conditions.This article reviews the recent lipidomic studies of physiological membrane adaptations of archaea,assesses the biomolecular basis of an organic paleothermometer,TEX86,and contemplates the future directions of archaeal lipidomics.The studies of extremophilic archaea have revealed that at least three different molecular mechanisms are involved in membrane adaptation of archaea:(1)regulation of the number of cyclopentane rings of caldarchaeol,(2)alteration of the diether-to-tetraether lipid ratio,and(3)variation of the proportion of saturated and unsaturated lipids.However,most of the studies have focused on a limited number of archaeal ether-linked lipids,such as glycerol dialkyl glycerol tetraethers(GDGTs),which only represent a fraction of the entire lipidome.Environmental factors such as growth temperature and pH have been most frequently reported,but biotic factors,including growth phases,nutrition,and enzymatic activities affecting the membrane lipid composition are often overlooked.Membrane lipids of mesophilic ammonia-oxidizing marine Thaumarchaeota have been applied in the reconstruction of past sea surface temperatures.However,recent culture-based physiological studies have demonstrated that non-thermal biotic factors,including dissolved oxygen,ammonia oxidation rate and the growth rate,are the main drivers of GDGT cyclization in Nitrosopumilus maritimus.Moreover,other related strains or ecotypes exhibit a markedly different set of stress adaptations.A trend is now developing to examine the whole lipid profile(lipidome)for studies of archaeal physiology and biochemistry related to lipid biosynthesis(lipidomics)to gain a better understanding of the biological mechanisms underpinning the applications of membrane lipid-based proxies in biogeochemical or ecological research.