| 英文摘要: | Earthquake nucleation, the process by which a fault transitions from locked to dynamically rupturing, remains poorly constrained due to limited observations. Understanding this process may help in determining how potential precursory earthquake processes, such as aseismic fault slip, can lead up to earthquake rupture. A number of observations support the hypothesis that slow earthquakes can precede hazardous regular earthquakes, but the transition process from slow to fast rupture has not been observed before. This project shows that the earthquake nucleation process can be observed in the lower crust of central Alaska, and that very low frequency earthquakes (VLFE's), a class of slow earthquakes, can transition directly into regular earthquakes. This research will undertake a thorough search for slow earthquake and earthquake nucleation signals throughout the Minto Flats Fault Zone in central Alaska, where a local dense seismic network is operating, with the ultimate goal of cataloging how these processes are related to regular earthquakes. Cataloging these processes in a single tectonic environment will allow us to model the earthquake nucleation process without needing to extrapolate results from disparate tectonic environments.
This project uses new, high quality observations of earthquake processes resulting from a dense deployment of seismometers in the Minto Flats Fault Zone of central Alaska, with the goal of characterizing slow earthquake occurrence and the relation between slow earthquakes and observed earthquake nucleation signals. Very few observations of VLFE's outside of subduction zone or plate boundary environments have been made, so the discovery of VLFE's on this intraplate fault system will expand our knowledge of where slow earthquakes are possible. VLFE's and nucleation signals identified to date occur at or below the deepest extent of regular seismicity along the fault zone, suggesting that the brittle-ductile transition plays an important role in nucleating earthquakes here. To characterize slow earthquake processes, the researchers employ correlation-based techniques to identify earthquake swarms, low frequency earthquakes, VLFE's, and foreshock sequences. Earthquake nucleation signals in central Alaska to date have been identified by chance, but this project will robustly catalog additional instances of nucleation signals by using correlation-based and seismological processing techniques. This work will quantify these signals in the Minto Flats Fault Zone and investigate their relation to regular earthquakes. In addition, this project will initiate a collaborative relationship between the observational seismology and the earthquake modeling communities, as a graduate student involved with observing nucleation signals will also work with leaders in the modeling community to conduct physics-based numerical modeling of the earthquake nucleation process. The earthquakes studied in this project, though small (at M~4), provide an observational bridge to larger earthquakes, which are hypothesized to have been preceded by slow earthquake processes. |