New Type of Earthquake Discovered
upstart writes:
New type of earthquake discovered:
To date, researchers have explained the occurrence of earthquakes in the hydraulic-fracturing process with two processes. The first says that the fluid pumped into the rock generates a pressure increase substantial enough to generate a new network of fractures in the subsurface rocks near the well. As a result, the pressure increase can be large enough to unclamp existing faults and trigger an earthquake. According to the second process, the fluid pressure increase from injection in the subsurface also exerts elastic stress changes on the surrounding rocks that can be transmitted over longer distances. If the stress changes occur in rocks where faults exist, it can also lead to changes that cause the fault to slip and cause an earthquake.
Recently, numerical models and lab analyses have predicted a process on faults near injection wells that has been observed elsewhere on tectonic faults. The process, termed aseismic slip, starts out as slow slip that does not release any seismic energy. The slow slip can also cause a stress change on nearby faults that causes them slip rapidly and lead to an earthquake. The lack of seismic energy from aseismic slip and the size of the faults involved make it difficult to observe in nature. Researchers have therefore not yet been able to document aseismic slip broadly with any association to induced earthquakes. The work of the current study, provides indirect evidence of aseismic loading, and a transition from aseismic to seismic slip.
The German-Canadian research team interpret the recently discovered slow earthquakes as an intermediate form of conventional earthquake and aseismic slip - and thus as indirect evidence that aseismic slip can also occur in the vicinity of wells. The researchers therefore dubbed the events hybrid-frequency waveform earthquakes (EHW).
Journal Reference:
Hongyu Yu, Rebecca M. Harrington, Honn Kao , et al. Fluid-injection-induced earthquakes characterized by hybrid-frequency waveforms manifest the transition from aseismic to seismic slip [open], Nature Communications (DOI: 10.1038/s41467-021-26961-x)
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