Did the 1999 earthquake swarm on Gakkel Ridge open a volcanic conduit? A detailed teleseismic data analysis

Abstract

In 1999, a seismic swarm of 237 teleseismically recorded events marked a submarine eruption along the Arctic Gakkel Ridge, later on also analyzed by sonar, bathymetric, hydrothermal, and local seismic studies. We relocated the swarm with the global location algorithm HY-POSAT and analyzed the waveforms of the stations closest to the events by cross-correlation. We find event locations scattered around 85 • 35 N and 85 • E at the southern rift wall and inside the rift valley of the Gakkel Ridge. Waveforms of three highly correlating events indicate a volumetric moment tensor component and highly precise referenced double-difference arrival times lead us to believe that they occur at the same geographical position and mark the conduit located further southeast close to a chain of recently imaged volcanic cones. This result is supported by station residual anomalies in the direction of the potential conduit. Seismicity is focused at the crust-mantle boundary at 16-20 km depth, but C. Riedel (B) · V. Schlindwein

Location and source mechanism of sound signals at Gakkel ridge, Arctic Ocean: Submarine Strombolian activity in the 1999–2001 volcanic episode

“…A detailed reconstruction of the seismic events in 1999 is given by Riedel and Schlindwein [2010]. Here we simply note that the character of the seismicity in 1999, the young lava on cratered Oden volcano and the ubiquitous presence of pyroclastic deposits make an explosive eruption in 1999 very likely.…”

“…Both theories have to be reviewed critically as they rely on preliminary earthquake locations with large epicenter uncertainties. Figure 1 shows a subset of relocated epicenters with an average location uncertainty of ±6.5 km [ Riedel and Schlindwein , 2010]. A temporal migration of the seismicity could not be confirmed.…”

Performance of localization algorithms for teleseismic mid-ocean ridge earthquakes: the 1999 Gakkel Ridge earthquake swarm and its geological interpretation

“…2(a) shows that most phases were recorded by stations which are between 30° and 60° away. As a consequence, the localization algorithms tolerate large traveltime residuals at the few near stations to better fit the abundance of large distance stations (Korger 2010; Riedel & Schlindwein 2010). These traveltime residuals probably result from an inadequate representation of heterogeneous upper‐mantle structure in 1‐D velocity models.…”

“…For localization we used the ak135 traveltime tables (Kennett et al 1995) combined with a regional velocity model for the 85°E/85°N volcanic complex (Table 1), which was compiled by Riedel & Schlindwein (2010). We localized first with a fixed hypocentre depth of 15 km, followed by an inversion for depth.…”

“…Based on USGS (United States Geological Survey) event locations, Tolstoy et al (2001) suggested that the 1999 Gakkel Ridge earthquake swarm resulted from magmatic pulses migrating along axis. Riedel & Schlindwein (2010) relocated the swarm using published phases by the comprehensive bulletin of the International Seismological Centre (ISC), but could not confirm the proposed migration of epicentres found by Tolstoy et al (2001).…”