Seismic tremor signals, also known as long-period, long-duration signals, have been reported in several locations where fluid injection for enhanced oil and gas exploration is taking place. However, the origin of these signals remains poorly constrained. We studied seismic tremor signals in Wellington Field, Kansas, using a seismic array during a carbon dioxide injection program. We show that these signals are generated

Slow earthquakes are an important part of a broad spectrum of the earthquake behavior. Yet, their underlying physics and connection to rest of the earthquake spectrum remain enigmatic. Taiwan is an area with complex geology hosting slow earthquakes. Still, their characteristics and relationship to other regular earthquakes are poorly understood. Using three years of high-quality seismic data, we have identified and located three discrete events known as very low-frequency earthquakes occurring deeper than the typical seismogenic zone in the earth crust. Our analyses show that these events modulate regular earthquakes in its vicinity. This relationship between the slow and fast earthquakes may be a result of fluid transfer from the deep to the shallow crust.

Various periodic external loading processes (e.g., snow, hydrological and atmospheric, earth tide and surface reservoir load, etc.) affect tectonic deformation and sometimes modulate seismicity in diverse tectonic settings. Small stress variations induced by external loads may influence the fault dynamics and destabilize fault zones. In this article, we report five cases of earthquake occurrence in the plate boundary and plate interior regions where such a destabilization seems to be operating. We test the possibility of resonance amplification assuming rate-and-state friction and look for the model parameters that could justify resonance destabilization. We find that frictional resonance destabilization is possible in regions that are near the stability boundary (velocity neutral areas). The critical slip distance for the evolution of friction is similar to laboratory estimates. In some cases, effective normal stress lower than the lithostatic stress have to be assumed for the model to be consistent with the observations, implying high pore pressure. We propose that crustal faults of conditionally stable frictional domains with anomalous pore pressure are sensitive to periodic stress perturbations by the external loading process.