New study links earthquakes, landslides and geothermal activity in North Iceland

A new study by geologists at the University of Iceland suggests that earthquakes and dikes have had a greater influence on the distribution and frequency of large landslides on the Tröllaskagi peninsula than previously thought.

The study also makes connections, for the first time, between the distribution of low-temperature geothermal fields, dikes and seismic activity in the Dalvík area. It suggests that the same geological forces govern all of these phenomena. The scientists point out that the so-called Dalvík Lineament has been responsible for historic earthquakes and they believe that powerful seismic activity in the area probably played a part in causing large landslides.

“This study highlights the fact that geothermal energy and natural hazards are two sides of the same coin. The same geological forces that create the conditions for valuable geothermal resources also influence where earthquakes occur and where large landslides originate,” says Gregory P. De Pascale, professor in structural geology and tectonics at the University of Iceland and co-author of an article published recently in the journal Landslides. The other author is Danielle Nicole Forester, who has a master's degree from the UI Faculty of Earth Sciences. Her master’s thesis explored the same topic and was part of this extensive research project. Danielle’s academic supervisor was in fact Gregory De Pascale.

This highlights how important it is to give students the chance to participate in research as part of their studies. Opportunities like this are one of the defining features of research universities like UI, which often allow students to work on research projects in collaboration with teaching and research staff.

Earthquakes may potentially reactivate older landslides

People in Iceland who follow news about volcanic eruptions and seismic activity will be familiar with references to dikes. Dikes form when magma flows into fractures in the Earth's crust. If the magma solidifies, a dike remains, marking the path the magma took through the crust.

“Three-dimensional models in the study indicate that the dikes and associated fractures play a key role in the distribution of geothermal heat in North Iceland. Where the fractures and dikes cut across dipping lava layers, they create pathways that can aid hot water pathways to the surface. In our view, this knowledge could become an important tool to help future exploration to find new geothermal resources,” says Gregory.

The article discusses, among other things, the Dalvík Lineament (DL) in North Iceland, seismic activity in the Tjörnes Fracture Zone (TFZ), geothermal areas and large Quaternary landslides. The results of the study indicate that the southern part of the TFZ is an active onshore seismic zone, and that large earthquakes can be expected in the area.

“Earthquakes like that could potentially reactivate older landslides, trigger new ones and even affect geothermal systems in the area,” says Gregory. “The DL is part of the active and complex tectonic plate boundary area of the TFZ, where tectonic movements cause strike-slip motion, extension and compression. The Dalvík area has been the site of major historical earthquakes, including the 1934 Dalvík Earthquake (Mw 6.3) and an offshore event in 1963 (Mw 7.0). Our study places these historical seismic zones in a broader context and suggests that seismic activity, fractures and dikes from prehistoric volcanism, as well as large landslides on the Tröllaskagi peninsula, are more closely linked than previously thought,” says the researcher.

Remote sensing and 3D models key to the research

UI is one of the world’s top universities for remote sensing, and it was used systematically in this study. Remote sensing is a set of methods that allow scientists to study the Earth’s surface remotely. These methods include satellite imagery, aerial photographs, drones and high-resolution digital elevation models used to analyse landscapes, geological formations and environmental changes.

The study used remote sensing imagery as well as digital elevation models, drone surveys, 3D models and field mapping to identify faults, dikes, landslides and other geological features in the area.

“One of our main findings,” says Gregory, “is that there was no clear evidence of a through-going fault scarp at the surface along the DL. Instead, the data suggest that seismic activity in the area is associated with north–south trending zones that coincide with the orientation of dikes on the Tröllaskagi Peninsula.”

Mapped hundreds of landslides

Gregory and Daniella mapped 367 landslides during the study. 174 of these were on the Tröllaskagi peninsula, covering a total area of 184 square kilometres, around 10% of the peninsula. Most of the landslides were within 20 kilometres of the median trace of the DL. When the results were compared with earlier mapping, the combined area of landslides proved to be 462.5 square kilometres.
“Our study shows that many of the landslides are located near dikes or have headscarps, or the top of a landslide, that coincide with such dikes. The dikes and the fractures they occupy cut across the regional lava pile and can affect rock strength, fracturing, permeability and slope stability.”

Landslides on the Tröllaskagi peninsula have previously been explained as the effects of glacial debuttressing (when a retreating glacier leaves behind destabilised slopes) and other topographical and climatic factors. The authors do not rule out these explanations, but argue that their data indicate that earthquakes and geological structures, particularly dikes, have also had a significant influence on where large landslides occurred and how frequent they were.

The study also has significant implications for geothermal research, as it sheds new light on the relationship between geothermal activity, fractures, dikes and seismic activity in North Iceland.

“Low-temperature geothermal fields on the Tröllaskagi Peninsula appear to align with dikes and areas of seismic activity. Thus, we believe that dikes and fracture systems control the flow of geothermal fluids in the subsurface, meaning that mapping such geological structures could support exploration to find additional low-temperature geothermal resources. Additionally this study has implications for planned tunnel projects in the area with faults, landslides, and earthquakes all being future challenges”.