Search

The Sipoholon geothermal field is located in North Sumatra, Indonesia. The geothermal field is characterized by 15 hot springs situated in the Tarutung pull-apart basin and an additional 8 hot springs outside of the basin. The main difficulty in understanding the geothermal system is the temperature distributions of the hot springs, which appears to be random, based on the occurrence of 3 inactive volcanoes around the basin. Here we report on preliminary results of two MT experiments that were carried out in Sipoholon, in December 2010 and July 2011. Data quality is generally good with the exception of sites from the populated basin area, which is noisier. Preliminary modeling results indicate a shallow high conductivity layer in the pull-apart basin area is generally caused by the sedimentary fill. Deeper conductive structure occurs east of the basin. Further data processing and modeling is necessary to decide if zones of high conductivity are related with a clay cap or hydrothermal fluids.

In recent years, 3D inversion has become a practical, if still computationally demanding, tool for interpreting MT data. This interpretation approach appears to hold great promise by overcoming the simplifications necessary to force the 3D nature of the real world into 2D models and thus producing more realistic and truthful images of the subsurface. In a series of geologic situations, however, we can identify a 2D regional structure in which local 3D structures are embedded. Based on synthetic data, we explore the resolution of an elongated highly conductive zone (HCZ) with varying along-strike extents embedded in a 2D regional resistivity structure with 3D and 2D inversion algorithms. Our results show that both inversion approaches recover the HCZ for large along-strike extents; for shorter extents, surprisingly 2D inversion better recovered the subsurface structures. In presence of high conductivity contrasts and wide conductivity contrasts 3D inversion can fail to resolve structures of predominantly 2D character. In 2D inversion, the weak 3D nature of the ocean included in the synthetic model impaired the impedance-only inversion results for short HCZ extent and problems occurred if phase values below 5° were present in the data set.

A Magnetotelluric (MT) field campaign was carried out in the SE Lower Saxony Basin, Germany, with the main goal of testing this method on imaging the regional Posidonia black shale sediments. Eightythree MT stations were deployed along a sixty-three kilometer long profile. Data was acquired successfully and we show examples of apparent resistivity and phase curves before and after remote reference processing. Also, in an attempt to correlate microscale with regional, macrosale electrical resistivity models, electrical resistivity measurements were made on a series of black shale samples from boreholes to study how electrical resistivity varies with different thermal maturity levels, organic carbon and mineral content, measurement orientation and water content. Results show that black shale conduct electrical currents highly anisotropic and that water content is a main controlling factor. So far, we cannot establish a simple correlation between electrical conductivity and intrinsic properties of black shale, like organic carbon, mineral composition, and thermal maturity.

Petroleum systems located at passive continental margins received increasing attention in the last decade mainly because of deep- and ultra‐deep-water hydrocarbon exploration and production. The high risks associated with these settings originate mainly from the poor understanding of inherent geodynamic processes. The new priority program SAMPLE (South Atlantic Margin Processes and Links with onshore Evolution), established by the German Science Foundation in 2009 for a total duration of 6 years, addresses a number of open questions related to continental breakup and post‐breakup evolution of passive continental margins. 27 sub‐projects take advantage of the exceptional conditions of the South Atlantic as a prime “Geo‐archive.” The regional focus is set on the conjugate margins located east of Brazil and Argentina on one side and west of Angola, Namibia and South Africa on the other (Figure 1) as well as on the Walvis Ridge and the present‐day hotspot of Tristan da Cunha. The economic relevance of the program is demonstrated by support from several petroleum companies, but the main goal is research on fundamental processes behind the evolution of passive continental margins.

Fast convergence between the oceanic Nazca and the continental South American plate is accommodated by recurrent rupture of large segments of the two plates’ interface. The resulting earthquakes are among the largest and, for their sizes, most frequent on Earth. Along the Chilean and southern Peruvian margin, all segments have ruptured at least once in the past 150 years for which there exist historic and/or instrumental records. The one segment that is most mature for re-rupture stretches for more than 500 km along the northernmost Chilean coast between roughly -23° and -18° latitude. It last broke in 1877 in a magnitude ~8.8 earthquake, triggering a major Tsunami. From the historical record, it has been known to have a recurrence cycle of approximately 110 years. The adjoining segments to the north and south broke rather recently in 1995 and 2001 in M>8 earthquakes and an M 7.7 earthquake encroached the southern part of the gap in 2007. The IPOC project intends to investigate this segment of the Nazca-South American plate boundary, on which a strong to devastating earthquake is expected to occur within the next years, by monitoring at a variety of time-scales deformation, seismicity, and magnetotelluric fields in the subduction zone at the closing stages of the interseismic cycle before and possibly during occurrence of a big earthquake. For that purpose, installation of long-term observatories in Northern Chile started in 2006 in a close cooperation of the Universidad de Chile (Santiago, Chile), the Universidad Catolica del Norte (Antofagasta, Chile), the Institut de Physique du Globe de Paris (Paris, France), and the German Research Centre for Geosciences (GFZ, Potsdam, Germany). Currently we are operating 14 modern seismological stations equipped with STS-2 broadband seismometers and accelerometers (EPI sensor). At least two more stations will be installed in the near future. To cope with the high resolution and dynamic of the sensors and data acquisition, site installation was accomplished with special care. At each station a cavern was blasted into the bedrock up to 5 meters deep to ensure stable conditions for measurements. Currently five stations are additionally recording continuously GPS signals, another five are also recording meteorological data, and another seven are equipped with Magneto-Telluric (MT) probes (fluxgate magnetometers and electrode lines). It is planned to extend the multi-parameter observation to as many stations as possible. So far ten of the stations are sending continuous data via satellite links (VSAT) to the GEOFON data host at the GFZ. We will be reporting first results on seismicity, transient deformation and MT from the first two years of recording.

ISSN: 0103-5053; International audience; The influence of the chemical structure of the mesogenic groups and the length of the spacer groups on the phase behavior in a series of side-chain liquid crystalline polyacrylates (SCLCP) have been studied using Small Angle X-ray Scattering (SAXS) and Polarized Optical Microscopy (POM). Analyses of the mesophase arrangement in unaligned and aligned samples by magnetic field are reported. The role of the spacer length on the local packing and on the thickness of the layers encountered in the SmA and SmC mesophases is elucidated. The tilt angles. of the mesogenic cores related to the normal of the layers in the SmC mesophases are measured. A study about the degree of order as a function of temperature for the smectic polymers was possible using SAXS measurements. A particular arrangement in one of the studied SCLCPs is related to the coexistence of two different phases.