Waveform Characteristics of Earthquakes Induced by Hydraulic Fracturing and Mining Activities: Comparison with Those of
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Original Paper
Waveform Characteristics of Earthquakes Induced by Hydraulic Fracturing and Mining Activities: Comparison with Those of Natural Earthquakes Nan Li,1,2 Baolin Li ,1,3,6 Dong Chen,1,3 Enyuan Wang,1,3 Yuyang Tan,4 Jiawei Qian,5 and Haishan Jia1,3 Received 5 February 2020; accepted 5 May 2020
Some industrial activities, such as underground mining, hydraulic fracturing (HF), can cause microearthquakes and even damaging earthquakes. In recent years, with the rapid development of mining and HF, many induced damaging earthquakes have been reported and studied. The seismic waves contain rich information of the seismic sources and wave propagation path, which are the valuable data for studying the natural and induced earthquakes. Therefore, the non-linear and time–frequency characteristics of different seismic waveforms are studied by using multifractal theory and the Hilbert–Huang transform method. In general, for both the natural and induced earthquakes, the larger the magnitude is, the longer the duration of the waveform is, and the lower the frequency is. In addition, the amplitude and frequency of natural and induced seismic wave show non-linear decreasing trend with the increase in propagation distance. Both the natural and induced earthquakesÕ waveforms show clear multifractal features. The multifractal parameters Da and Df(a) can be used as indicators to reflect the non-linear characteristics of the seismic waveforms. The seismic waveformsÕ multifractal and time–frequency characteristics recorded by the specific sensors are affected by not only the magnitudes, types and rupture mechanism of seismic sources, but also the distances from sensors to seismic sources, wave propagation path and the sensors’ properties. Because the coal is soft and unconsolidated rock with developed joints and fractures, the seismic waveforms induced by mining are more complex and variable than the ones with the same magnitude induced by HF of shale and hot dry rock. KEY WORDS: Natural earthquakes, Induced earthquakes, Seismic waveform, Multifractal characteristic, Time–frequency analysis.
1
State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology, Xuzhou 221116, Jiangsu, China. 2 School of Mines, China University of Mining and Technology, Xuzhou 221116, Jiangsu, China. 3 School of Safety Engineering, China University of Mining and Technology, Xuzhou 221116, Jiangsu, China. 4 Key Laboratory of Submarine Geoscience and Prospecting Techniques MOE, Ocean University of China, Qingdao 250100, Shandong, China. 5 School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230000, Anhui, China. 6 To whom correspondence should be addressed; e-mail: [email protected]
INTRODUCTION Earthquake is a common and widespread natural phenomenon around the world. The statistics show that earthquakes with moment magnitude larger than 5.0 (MW > 5.0) occur about 2000 times every year around the world. Earthquakes, especially the strong earthquakes, are the serious natural d
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