Micrometre-scale deformation observations reveal fundamental controls on geological rifting

Abstract

Many of the world’s largest volcanic eruptions are associated with geological rifting where major fractures open at the Earth’s surface, yet fundamental controls on the near-surface response to the rifting process are lacking. New high resolution observations gleaned from seismometer data during the 2014 Bárðarbunga basaltic dyke intrusion in Iceland allow us unprecedented access to the associated graben formation process on both sub-second and micrometre scales. We find that what appears as quasi steady-state near-surface rifting on lower resolution GPS observation comprises discrete staccato-like deformation steps as the upper crust unzips through repetitive low magnitude (MW < 0) failures on fracture patches estimated between 300 m2 and 1200 m2 in size. Stress drops for these events are one to two orders of magnitude smaller than expected for tectonic earthquakes, demonstrating that the uppermost crust in the rift zone is exceptionally weak.

Tremor-rich shallow dyke formation followed by silent magma flow at Bárðarbunga in Iceland

“…Once the subaerial ssure opened no tremor is detected along the dyke feeding it. This observation is further supported by a short term deployment directly on an already formed surface fracture zone directly on/above the dyke (station DY3 16 , black triangle in Figure 1, gure 3a and supplementary gure 5). No tremor is evident.…”

Relating gas ascent to eruption triggering for the April 27, 2016, White Island (Whakaari), New Zealand eruption sequence

“…Hence, we band-passfiltered the horizontal components between 0.03 Hz and 0.1 Hz. In order to preserve the static offset on the vertical components, we low-pass-filtered them below 0.1 Hz and applied a 100-s-long median filter in order to stabilize the observed displacement step (see Thun et al 2015Thun et al , 2016. The filtered displacement waveforms are shown in Fig.…”

Dynamic strain determination using fibre-optic cables allows imaging of seismological and structural features

“…In addition, dynamic stress from remote earthquakes has also been proposed as a mechanism to trigger volcanic eruptions, earthquakes, as well as micro-seismic activity 9 , and may also explain inelastic ground response in compliant fault zones 10 . Micrometre-scale deformation at faults were inferred from GPS and broadband seismological observations during the Barðabunga volcanic eruption in Iceland 11 . However, imaging the internal structure of faults with high resolution as well as inferring creeping processes of faults at sub-micrometre steps remains challenging 3 .…”