Monitoring of Relative Velocity Change at the Lassen Volcanic Center

Temporal Evolution in Seismic Velocity¶

We estimate relative velocity changes (dv/v) by using MSNoise [Lecocq et al., 2014]. Following Brenguier et al. [2008] and Taira et al. [2015], our analysis focuses on waveforms in a frequency range of 0.1-0.9 Hz. A set of 4 seismic stations (stations LDH, LEL, LME, LRR) is used based on the high rate of data completeness. We determine the reference Green’s function (GF) for each station pair as the average of 1-day GFs obtained in the time interval, January 2012 through April 2016. The time history of dv/v is determined by measuring delay times between 5-day stacks of GFs and the reference GF.

We include horizontal component data for the dv/v measurement. The maximum available number of channel pairs (e.g., ZZ, ZN, ZE) is 12. To monitor the relative velocity change, we implement an automated system that updates the time history of dv/v shown in Figure 1. This automated process makes use of waveforms archived at the Northern California Earthquake Data Center [NCEDC, 2014]. Figure 1 is currently updated every day. Our monitoring system finds a 0.1% velocity reduction in late May 2013, which is most likley due to dynamic stress changes from the magnitude 5.7 Greenville earthquake.

Figure 1. Result of the relative velocity change (dv/v) for the last 2 years. Top panel shows the number of channel pairs used to infer dv/v. The bottom panel shows the time history of dv/v. The error bars represent the two-sigma standard deviation. Result for the dv/v time series from January 2012 to current is here.

Map View¶

Figure 2. Map view of seismic stations from the Northern California Seismic Network operated by U.S. Geological Survey. Red line indicates the boundary of the Lassen Volcanic National Park.