| 英文摘要: | Earthquakes remain one of the major natural hazards that cause human and financial losses. High levels of earthquake hazards are generally expected at plate boundaries, such as the "Ring of Fire" along the Pacific Rim. However in the last five years, earthquakes in the interior of continents are rapidly increasing. Most of the increases are attributed to the development in oil/gas exploration, and the associated wastewater disposal into deep formations (i.e., other than the formations that produce oil and gas). For this reason, most of the new events are termed as "induced earthquakes" as they are closely related to human activities. The state of Oklahoma has been known as "the new earthquake capital" (more precisely, "the earthquake capital of man-made earthquakes"), with earthquake rates of M larger than 3 exceeding those in California. On February 13, 2016, a M=5.1 earthquake occurred near Fairview, Oklahoma, being the third largest event in the history of the state. The fault that hosted this earthquake had experienced seven M4 earthquakes in the past four months. Local residents reported strong ground-shaking, gradual accumulation of energy (foreshocks), cracks in the house, and more importantly, concerns about safety. The soil in this area is mostly sand (featured with the Little Sahara State Park), which tend to make building foundations unstable, and potential hazard of liquefaction and landslides. This RAPID proposal aims at recording the seismic activity in this region to better understand its cause and ultimately its hazard potential.
With this proposal, we will deploy 10 broadband stations that will provide a dense azimuthal coverage to the western Oklahoma area, in particular around the Fairview and Woodward faults. These faults are separated by only about 8 km, but have distinct seismicity characteristics - the Fairview fault has predominately individual aftershock sequences from M4 events, while the Woodward fault has mostly small earthquakes with gradual seismicity rate changes, they also have different types of correlation with injection volume changes. The data collected will help to address scientific questions such as: (1) What is the relationship between seismogenic faults mapped from seismicity and geological mapped faults from outcrops and active seismic survey? What do they reveal about the faulting processes? (2) Does injection volume variations influence the maximum size of induced earthquakes? If so, what could be suggested for the volume reduction procedures to mitigate man-made earthquake hazards? (3) Are there resolvable differences in fault mechanisms between the two major faults in this area, which would lead to significantly different seismic responses to fluid injection, e.g., velocity structures, fault strength or fault orientation relative to in-situ stress field? The results will provide important parameters that would help to assess earthquake hazards associated with ground shaking and other secondary hazards, such as liquefaction or landslides. |