Regional controls on volcano seismicity along the Aleutian arc

Abstract

We identify patterns in volcano seismicity along the Aleutian arc using nearly 10 years of seismic data recorded at 46 volcanoes. The volcanoes in the central portion of the arc-those located from Aniakchak to Okmok-are associated with significantly more seismicity at depths below 15 km. We also examine the median weight percent SiO 2 compositions of the seismically monitored volcanoes by compiling published geochemical data. We find that the transition between felsic volcanism in the east to more mafic volcanism in the west occurs in the same region where the depth distribution of volcanic earthquakes changes. Since deep volcanic earthquakes are often thought to be generated by the ascent of magma through the deep crust (i.e., depths > 15 km), our results suggest that magma ascent is more prolific in the central part of the arc compared to the western and eastern regions. This observation is in agreement with the location of the largest and most historically active volcanoes in the Aleutian arc, which are found in same region that generates abundant deep volcano seismicity. We propose two models to explain these apparent variations in magmatic flux: (1) a stress-based model, in which subduction obliquity and the collision of the Yakutat block affect the stress regime in the upper plate, inhibiting the rise of magma in eastern and western regions of the arc and (2) a melt-based model, where more magma is generated in the central region of the arc through increased H 2 O in the downgoing slab via water-laden sediments and subducting fracture zones.

Alaska Volcano Observatory Alert and Forecasting Timeliness: 1989–2017

“…This number has increased from three (in 1989), and has fluctuated based on individual network health. For this analysis, events are considered seismically monitored if the volcano has a local seismic network, comprised of four or more seismometers, operating at the time of the event, and operating with sufficient time before the event in order to characterize background seismicity, following Buurman et al (2014) and Pesicek et al (2018). Events with a local seismic network and not formally listed as monitored by AVO (often due to insufficient time to categorize background seismicity, e.g., Pavlof, 1996) are marked "YES-unofficial" in Table 1.…”

“…Although many events in our list barely meet this standard, other volcanoes have more dense seismic networks with as many as 17 instruments [Spurr has 17; Okmok and Akutan follow with 13], allowing for better detection of subtle seismic precursors . Seismic monitoring status at time of event is based on network health analyses by Pesicek et al (2018) and Buurman, et al (2014). For those events with seismic monitoring, we also briefly examine whether or not precursory seismicity was detected by our network, as do Pesicek et al (2018).…”

Gas Emissions From the Western Aleutians Volcanic Arc

“…Plate convergence is near orthogonal in the eastern and central portion of the arc and gradually becomes more oblique in the western region of the Aleutian Arc, with plate motion eventually transitioning to strike-slip near ∼170 °E (Figure 1) (DeMets et al, 1990;Buurman et al, 2014). The varying convergence angles, combined with the thickness of subducted sediment, result in highly variable subducted sediment fluxes along the length of the arc, with a maximum in the central Aleutians and a minimum in the western Aleutians (Kelemen et al, 2003).…”

Prevalence of Seismic Rate Anomalies Preceding Volcanic Eruptions in Alaska

“…The background time period for each volcano is defined by the number of days of seismic monitoring minus eruptive periods and network outages. To determine seismic network outages, we use the results of the AVO network health analysis by Buurman et al (2014) for the period October 2002 through December 2011 and perform our own similar analysis of the continuous seismic data to define outages since 2012. Network outages are defined as periods when less than four stations within 30 km of a volcano were transmitting data.…”