ALBERT

Beschreibung: The Powell Basin is a small oceanic basin bounded by continental blocks that fragmented during drifting of South America from Antarctica. The basin is limited to the east by the South Orkney Microcontinent, to the north by the South Scotia Ridge, and to the west by the Antarctic Peninsula. The timing of its opening is poorly constrained due to low amplitude magnetic anomalies which hampers their identification and cause large uncertainties in proposed ages that range from the Late Eocene to Early Miocene. The Powell basin has been extensively studied using a variety of geophysical methods including seismic, gravity and magnetic surveys intended to unveil the tectonic domains. The magnetic anomalies and the thermal regime of the basin are of particular interest, as some of these studies have suggested that the absence of clear seafloor magnetic anomalies is the result of impermeable layers that prevent the venting of hot fluids into the water column. Using new magnetic and heat flow data together with geophysical data from international databases, we analyze the thermal structure of the Powell Basin its lithosphere and the upper mantle dynamics and discuss the probable causes of the abnormally small amplitudes of magnetic anomalies.

Beschreibung: The 2021 Tajogaite eruption in La Palma, Canary Islands, was accompanied by strong volcanic tremor. In September 2021, during the first two weeks of eruption, we deployed two small-aperture seismic arrays. We chose two locations around Montaña Caldero and Llano del Jable, located about 4 km SE and 2 km NE of the eruption site. The arrays were composed of 1 three-component and 9 vertical-component short-period seismometers, sampled at 100 sps by a 12-channel data acquisition system. In each array, the receivers were spread with an aperture of about 400 m. Although they operated intermittently due to failures in the power supply related to ash fall, they provided long time series of multichannel seismic data that allow for the characterization of the syn-eruptive tremor. The analysis of the recorded wavefields reveals a persistent tremor source linked to the activity of the eruptive vents. The main component of the wavefield in the 1-3 Hz frequency band propagates with apparent slowness around 1 s/km, impinging on the arrays from directions of ~300 and 260ºN, respectively. These directions are slightly deviated from the active vents azimuths, a fact that we attribute to propagation effects produced by the topography and heterogeneous velocity structure. Subtle variations in the apparent slowness and propagation azimuths are investigated using the relative slowness estimate method, that allows for a precise determination of the apparent slowness vectors.

Beschreibung: The Powell Basin is a small oceanic basin bounded by continental blocks that fragmented during break up of Antarctica from South America. This basin bounds the South Orkney Microcontinent to the east, the South Scotia Ridge to the north, and the Antarctic Peninsula to the west. The timing of its opening is poorly constrained due to the low amplitude of the oceanic spreading magnetic anomalies which hampers their identification and interpretation causing large uncertainties in proposed ages that range from the Late Eocene to Early Miocene. This basin has been extensively studied using a variety of geophysical methods including seismic, gravity and magnetics surveys intended to unveil the tectonic domains, the particularities of its magnetic anomalies and the understanding of the thermal regime in this area. Here, we show new magnetic and heat flow data integrated with other geophysical data from international databases (multichannel seismic data, bathymetry and free-air gravity), to analyze the thermal structure of the lithosphere of Powell Basin and the upper mantle dynamics as well as to discuss the probable causes of the abnormally small amplitudes of its magnetic anomalies. Our results show that the low magnetic anomaly amplitudes are not widespread but concentrate in the eastern and southwestern part of the basin. We propose that these small amplitudes result from the thermal dependency of magnetic rocks caused by an asthenospheric branch flow that penetrates the Powell Basin through the northern area.