Geology topics

Xiangfang Zeng

Publications and source records attributed to Xiangfang Zeng.

3 recordsLinked to original sources

USGS2018

Inferring magma dynamics at Veniaminof volcano via application of ambient noise

Ambient noise interferometry has become an increasingly popular tool for monitoring active volcanoes. We apply this method to investigate seven past eruptive periods at Veniaminof volcano, Alaska. Two of the largest eruptions studied show seismic velocity changes associated with preeruptive , coeruptive, and posteruptive volcanic processes. We develop and implement new analysis techniques to determine how seismic velocity changes at Veniaminof are distributed with depth. Spatiotemporal examination of these seismic velocity changes reveals evidence for the distribution of magma storage and the timescale at which magmatic fluids intrude into and reside within these storage regions in the months preceding eruption. We conduct the depth analysis using data recorded on a single seismometer. The same analysis could be applied to any volcano monitored by at least one seismometer in order to detect magmatic activity indicative of impending eruption, specifically the intrusion and migration of magmatic fluids into the volcanic system.

Alaska↗

USGS2016

3-D P- and S-wave velocity structure and low-frequency earthquake locations in the Parkfield, California region

To refine the 3-D seismic velocity model in the greater Parkfield, California region, a new data set including regular earthquakes, shots, quarry blasts and low-frequency earthquakes (LFEs) was assembled. Hundreds of traces of each LFE family at two temporary arrays were stacked with time–frequency domain phase weighted stacking method to improve signal-to-noise ratio. We extend our model resolution to lower crustal depth with LFE data. Our result images not only previously identified features but also low velocity zones (LVZs) in the area around the LFEs and the lower crust beneath the southern Rinconada Fault. The former LVZ is consistent with high fluid pressure that can account for several aspects of LFE behaviour. The latter LVZ is consistent with a high conductivity zone in magnetotelluric studies. A new Vs model was developed with S picks that were obtained with a new autopicker. At shallow depth, the low Vs areas underlie the strongest shaking areas in the 2004 Parkfield earthquake. We relocate LFE families and analyse the location uncertainties with the NonLinLoc and tomoDD codes. The two methods yield similar results.

California↗

USGS2016

Along-strike variations in fault frictional properties along the San Andreas Fault near Cholame, California from joint earthquake and low-frequency earthquake relocations

Recent observations of low‐frequency earthquakes (LFEs) and tectonic tremor along the Parkfield–Cholame segment of the San Andreas fault suggest slow‐slip earthquakes occur in a transition zone between the shallow fault, which accommodates slip by a combination of aseismic creep and earthquakes (<15  km depth), and the deep fault, which accommodates slip by stable sliding (>35  km depth). However, the spatial relationship between shallow earthquakes and LFEs remains unclear. Here, we present precise relocations of 34 earthquakes and 34 LFEs recorded during a temporary deployment of 13 broadband seismic stations from May 2010 to July 2011. We use the temporary array waveform data, along with data from permanent seismic stations and a new high‐resolution 3D velocity model, to illuminate the fine‐scale details of the seismicity distribution near Cholame and the relation to the distribution of LFEs. The depth of the boundary between earthquakes and LFE hypocenters changes along strike and roughly follows the 350°C isotherm, suggesting frictional behavior may be, in part, thermally controlled. We observe no overlap in the depth of earthquakes and LFEs, with an &sim;5  km separation between the deepest earthquakes and shallowest LFEs. In addition, clustering in the relocated seismicity near the 2004 M w 6.0 Parkfield earthquake hypocenter and near the northern boundary of the 1857 M w 7.8 Fort Tejon rupture may highlight areas of frictional heterogeneities on the fault where earthquakes tend to nucleate.

California↗