A high-resolution seismic catalog for the 2021 MS6.4/MW6.1 Yangbi earthquake sequence,Yunnan, China: Application of AI picker and matched filter          下载免费PDF全文

Yijian Zhou  Abhijit Ghosh  Lihua Fang  Han Yue  Shiyong Zhou  Youjin Su 《地震科学（英文版）》2021,34(5):390-398

We present a high-resolution seismic catalog for the 2021 M_S6.4/M_W6.1 Yangbi sequence. The catalog has a time range of 2021-05-01 to 2021-05-28, and contains ~8,000 well located events. It captures the features of the whole foreshock sequence and the early aftershocks. We designed a detection strategy incorporating both an artificial intelligent (AI) picker and a matched filter algorithm. Here, we adopt a hybrid AI method incorporating convolutional and recurrent neural network (CNN & RNN) for event detection and phase picking respectively (i.e. CERP), a light-weight AI picker that can be trained with small volume of data. CERP is first trained with detections from a STA/LTA and Kurtosis-based method called PAL, and then construct a rather complete template set of ~4,000 events. Finally, the matched filter algorithm MESS augments the initial detections and measures differential travel times with cross-correlation, which finally results in precise relocation. This process gives 9,026 detections, among which 7,943 events can be well relocated. The catalog shows as expected power-law distribution of frequency magnitude and reveals detailed pattern of seismicity evolution. The main features are: (1) the foreshock sequence images simple fault geometry with consistent strike, but also show a variable event depth along strike; (2) the mainshock ruptures the same fault of the foreshock sequence and activate conjugate faults further to the southeast; (3) complex seismicity are developed in the post-seismic period, indicating complex triggering mechanisms. Thus, our catalog provides a reliable basis for further investigations, such as b-value studies, rupture process, and triggering relations.  相似文献   

Effects of mooring line drag damping on response statistics of vessels excited by first- and second-order wave forces     

A. Sarkar  R. Eatock Taylor 《Ocean Engineering》2000,27(6):17

The drag-induced damping in a mooring cable due to combined first- and second-order wave excited motion of a moored vessel has been determined by statistical linearisation. A dynamic stiffness approach developed elsewhere is used to deal with the dynamics of the mooring cables. The power spectral densities of low- and wave-frequency responses are obtained which clearly show the influence of mooring line damping. The non-Gaussian probability density functions (pdf) and expected crossing rates of vessel responses and dynamic cable tensions are determined using the Kac–Seigert technique, and the influence of drag damping is highlighted.  相似文献   

Wind dependence of quasi-specular sea scatter     

Abhijit Sarkar  Lakshmi Bhaduri 《Journal of Earth System Science》1984,93(2):111-116

Earlier investigations have shown that a power law relationship of the typeσ=aW ^b exists between the scattering coefficientσ and sea surface wind speedW at microwave frequencies. The coefficientsa andb are usually quoted for different frequencies, look angles, polarizations etc. This paper attempts to define the angular dependence using such a power law relationship in the quasi-specular range.  相似文献   

Effects of geomagnetic storms on the sunrise fade of long distance 40 kHz signals     

B. K. De  S. K. Sarkar 《Meteorology and Atmospheric Physics》1986,35(4):227-235

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On absence of certain periods in the love-wave spectrum     

Gopi Nath Sarkar 《Pure and Applied Geophysics》1964,58(1):41-48

Summary It has been noted by several observers that no Love-wave spectrum is complete in the sense that it contains all the periods. The reason for this has been sought for in the presence of a low-velocity layer.  相似文献   

Very low frequency atmospheric radio noise field intensities     

A. K. Sen  A. B. Bhattacharya  S. K. Sarkar 《Meteorology and Atmospheric Physics》1982,31(3):263-268

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Seasonal Behaviour of the Afternoon Maximum of a Long-Distance 40 kHz Signal     

De  B. K.  Sarkar  S. K. 《Studia Geophysica et Geodaetica》1997,41(4):382-390

The afternoon maximum (AMX) observed in 40 kHz signal strength, propagated over a distance of 5100 km in the low latitudes of the Northern Hemisphere, exhibits an appreciable asymmetric decrease in its time of occurrence about June-July. The time of occurrence of the AMX of this low-latitude E-W propagation follows the sunset lime equation at the centre of the propagation path. A significant test shows a high correlation of the absence of the AMX with geomagnetic storms. The extra-ionizations in the ionospheric D region during geomagnetic storms may lead to the absence of the afternoon maximum.  相似文献   

Comparison of two potential strategies of planktonic foraminifera for house building: Mg or H removal?     

Richard E Zeebe  Abhijit Sanyal 《Geochimica et cosmochimica acta》2002,66(7):1159-1169

Marine organisms must possess strategies enabling them to initiate calcite precipitation despite the unfavorable conditions for inorganic precipitation in surface seawater. These strategies are poorly understood. Here we compare two potential strategies of marine calcifyers to manipulate seawater chemistry in order to initiate calcite precipitation: Removal of Mg²⁺ and H⁺ ions from seawater solutions. An experimental setup was used to monitor the onset of inorganic precipitation on seed crystals as a function of the Mg²⁺ concentration and pH in artificial seawater. We focused on precipitation rates typical for biogenic calcification in planktonic foraminifera (∼10⁻³ mol m⁻² h⁻¹) and time scales typical for the initiation of calcification in these organisms (minutes to hours). We find that the carbonate ion concentration has to increase by a factor of ∼13 when [Mg²⁺] increases from 0 to 53 mmol kg⁻¹ in order to maintain a typical biogenic precipitation rate. Model calculations for the energy requirement for various scenarios of Mg²⁺ and H⁺ removal including Ca²⁺ exchange and CO₂ diffusion are presented. We conclude that the more cost-effective strategy to initiate calcite precipitation in foraminifera is H⁺ removal, rather than Mg²⁺ removal.  相似文献   

Oxygen and carbon stable isotope studies onGloborotalia menardii from Pleistocene DSDP Cores in northern Indian Ocean and their paleoclimatic and paleoceanographic implications     

Ashish Sarkar  Asit K Guha  Supriyo Chakraborty 《Journal of Earth System Science》1996,105(2):119-129

Stable isotope ratios of oxygen (δ¹⁸O) and carbon (δ¹³C) in tests ofGloborotalia menardii from samples at 25 cm intervals of top 900 cm cores, representing different thicknesses of the Pleistocene, from DSDP Sites 219, 220 and 241 in the northern Indian Ocean have been measured. Based on the δ¹⁸O stratigraphy, glacial and interglacial phases during the Pleistocene have been recognized, which are in good agreement with the standard Quaternary planktonic foraminiferal/climatic zones i.e., Ericson zones at these sites, based onG. menardii abundances. The GIA (glacial interglacial amplitude) at Sites 241, 219 and 220 are of the order of 1·2, 1·4 and 1·9‰ respectively. The last glacial and interglacial maxima (18 ka BP and 125 ka BP respectively) could be identified in DSDP Cores 241, and 219 with some precision. ‘Isotopic ages’ could be assigned to the different levels of these core sections based on the correlation of δ¹⁸O record from these sites with the SPECMAP record (Imbrieet al 1984). Changes in sediment accumulation rates at different levels of the Pleistocene have been worked out on the basis of changes in oxygen isotopic ratio. Oscillations in δ¹³C stratigraphy at Site 241 indicated southwest monsoon induced increase in upwelling and productivity during warmer periods. At Sites 219 and 220, variations in the δ¹³C record were due to the mixing of bottom water.  相似文献   

On the effect of discontinuity in boundary gradient or in material properties on propagation of elastic waves     

Gopinath Sarkar 《Pure and Applied Geophysics》1966,63(1):5-10

Summary The effect of surface irregularities in the form of boundary discontinuous gradients has been studied. It has been shown that certain waves will be attenuated due to passage through such irregularities in internal structure.  相似文献