Automatic microseismic events detection using morphological multiscale top-hat transformation

The occurrence of microseismic is not random but is related to the physical properties of the underground medium.Due to the low intensity and the influence of noise,microseismic eventually lead to poor signal-to-noise ratio.We proposed a method for automatic detection of microseismic events by adoption of multiscale top-hat transformation.The method is based on the difference between the signal and noise in the multiscale top-hat transform section and achieves the detection on a specific section.The microseismic data are decomposed into different scales by multiscale morphology top-hat transformation firstly.Then the potential microseismic events could be detected by picking up the peak value in the multiscale top-hat section,and the characteristic profile obtains the start point with a specific threshold value.Finally,the synthetic data experiences demonstrate the advantages of this method under strong and weak noisy conditions,and the filed data example also shows its reliability and adaptability.

Study on the Physical Process and Seismogenic Mechanism of the Yangbi MS 6.4 Earthquake in Dali,Yunnan Province

The Ms 6.4 earthquake occurred on May 21,2021 in Yangbi County,Dali Prefecture,Yunnan Province,which was the largest earthquake after the 2014 Jinggu Ms 6.6 earthquake,in western Yunnan.After the earthquake,the rapid field investigation and earthquake relocation reveal that there was no obvious surface rupture and the earthquake did not occur on pre-existing active fault,but on a buried fault on the west side of Weixi–Qiaohou–Weishan fault zone in the eastern boundary of Baoshan sub-block.Significant foreshocks appeared three days before the earthquake.These phenomena aroused scholars'intensive attention.What the physical process and seismogenic mechanism of the Yangbi Ms 6.4 earthquake are revealed by the foreshocks and aftershocks?These scientific questions need to be solved urgently.

The seismogenic structures and migration characteristics of the 2021 Yangbi M6.4 Earthquake sequence in Yunnan,China

We constructed a more complete earthquake catalog in the 2021 Yangbi M6.4 focal area by re-scanning the continuous waveforms integrated with deep learning and template matching techniques,to explore the seismogenic structures of the Yangbi mainshock and its nucleation process.The new catalog has three times the number of earthquakes than the CENC catalog,and the magnitude completeness has dropped from 1.1 to 0.5.The distribution of earthquakes indicates a broom-shaped structure consisting of several oblique secondary faults and a strike-slip main fault which strikes to 315°with 80°dipping to NE.The earthquakes extend along the fault strike about 27 km in width and 2-13 km at depth and have noticeable variations on seismicity in the mainshock’s north and south.Compared with the north,the south has denser and higher magnitude aftershocks and also has a seismic gap probably weakened by the fluid at the depth range of about 5-6 km.The foreshocks were mainly active in the 8-kilometer-long fault zone south of the mainshock,which show a steady drop in b-values over time and a migration pattern toward the epicenter of two steep jumps,stagnation,and then acceleration which finally triggered the mainshock.While in the north,seldom foreshock occurred,and the aftershocks were delayed triggered 3 hours after the mainshock,and sparsely scattered shallow at depth and small in magnitude.To summarize,the northern part of the Yangbi seismogenic fault is thought to be relatively locked,whereas the southern part has a weakening zone and promotes pre-slip.The nucleation mechanism of the mainshock and its onset at the junction of the locked and pre-slip zones may be a combination of pre-slip and cascade triggering.