Abstract
AbstractRepeated periods of inflation‐deflation in the vicinity of Mt. Þorbjörn‐Svartsengi, SW‐Iceland, were detected in January–July, 2020. We used seismic ambient noise and interferometry to characterize temporal variations of seismic velocities (dv/v, %). This is the first time in Iceland that dv/v variations are monitored in near real‐time during volcanic unrest. The seismic station closest to the inflation source center (∼1 km) showed the largest velocity drop (∼1%). Different frequency range measurements, from 0.1 to 2 Hz, show dv/v variations, which we interpret in terms of varying depth sensitivity. The dv/v correlates with deformation measurements (GPS, InSAR), over the unrest period, indicating sensitivity to similar crustal processes. We interpret the velocity drop to be caused by crack opening triggered by intrusive magmatic activity. We conclude that single‐station cross‐component analyses provide the most robust solutions for early detection of magmatic activity.
Highlights
The Reykjanes peninsula (RP) in SW Iceland is an oblique spreading rift marking the plate boundary between the North American and the Eurasian plates
Several volcanic systems make up the RP, that is, Reykjanes (RVS) which last erupted in 1240 CE and Krýsuvík (KVS) (Clifton & Kattenhorn, 2006; Larsen & Guðmundsson, 2016; Sæmundsson et al, 2020)
We find that positive dv/v tends to peak in the RP during the summer (Figure S1a) since the changes in groundwater level (GWL) and snow load contribution to stresses are considerably less in this coastal region compared to ice-covered areas
Summary
The Reykjanes peninsula (RP) in SW Iceland is an oblique spreading rift marking the plate boundary between the North American and the Eurasian plates. In January 2020, surface deformation was detected by GPS and InSAR observations with the center of uplift located ∼2 km west of Mt. Þorbjörn, indicating magmatic inflation (Geirsson et al, 2020). Þorbjörn, indicating magmatic inflation (Geirsson et al, 2020) This is the first time such a signal has been recorded in the Reykjanes volcanic system. At the time of revising this report, intense seismic activity and deformation is observed in Fagradalsfjall (a part of KVS), which resulted in an effusive eruption in Geldingadalir valley on March 19, 2021 (see Figure 1a). We focus on the recent unrest (January–July 2020) in Mt. Þorbjörn-Svartsengi, which offers a tangible case study for examining seismic velocity changes over time in response to a series of repeated magmatic intrusions in the RP. Our primary objective is to use ANSI in near-real-time to characterize temporal velocity changes to track the physical changes in the medium related to the unrest
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