Vulnerability and risk assessment for geohazards

Earthquake hazard, risk and loss

Stability of rock slopes

Geomechanical modelling

Offshore geohazards

SafeLand (Landslide risk in Europe)

Slide dynamics

Tsunami modelling and prediction

Remote sensing, monitoring and early warning systems

Geophysics for geohazards

Application of GIT to geohazards

Prevention and mitigration

IYPE projects related to ICG

www.snoskred.no
Norwegian snow avalanche website

2nd ICG Phd seminar
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Positive midway evaluation of ICG
 

Submarine Mass Movements and Their Consequences
 

4th International Symposium
on Submarine Mass Movements and Their Consequences,
Austin Texas, 2009

EGU 2009

OTC Geohazard Session
 Download abstracts
 

Debris flow and river flooding 23 Aug 2005 in Paznauner Valley, Tirol, Austria

BAM Earthquake of 26th of December 2004

ECI Conference: Geohazards - Technical, Economical and Social Risk Evaluation

2nd International conference on Submarine Mass Movement and Their Consequences 2005

International Workshop 27th of September 2004 - Natural Disaster Hotspot
 

Introduction

ICG introduced "Themes" in 2005 for topics going across several projects and for which coordination was necessary, this for several reasons

• Better use of human and equipment resources, and better communication
• Spreading of competency between the projects
• Identification of research topics and project work for students
• Publications

At ICG all projects are multi-disciplinary, covering geology, geotechnics and geophysics. In many cases, techniques that were used in one project, and possibly improved, are useful in other projects as well. It is therefore important to keep an overview of what is going on in each project to better cover the need in other projects. Geophysics is needed to give information about the underground structures, especially for spatial mapping. ICG Theme 1 is dedicated to the use of "Geophysics in Geohazards" assessments, on land and offshore.

Many geophysical techniques can be applied, depending of the type of structures to study

•  Seismic reflection and refraction
•  Microseismic monitoring
•  Ground Penetrating Radar (GPR)
•  Electrical methods
•  Electromagnetism
•  Magnetism
•  Gravimetry

Of all available techniques, only those able to give useful information to geologists and geotechnicians faced to geohazard assessment will be studied within ICG.
Click here for more information about the use of geophysics (Quality Guidelines for Geophysical Methods, Swiss Geophysical Commission). 
 

Content
Click on the bullet points below to be directed to the sub chapters

• Objectives
• National and international cooperation
• Past and current activities:

  SoA

  Quick clay and resistivity

  Åknes rock slide

  Monitoring of railroad line

  Flatbre moraine test site

  Glacier hazards in Caucasus

  inSAR

  GinSAR

  S-wave and shallow sediments offshore

  Finneidfjord

  Trondheim Harbour

• Equipment
• Education
• Staff
• Publications

Objectives

The scientific objectives within the Geophysics for Geohazards Theme are:

•  To improve the integration of different data types (geological, geotechnical and geophysical) in geohazard investigations by maintaining an open dialog between the different experts and working closely with the relevant ICG projects
•  To identify specific research areas for geophysics, taking into account the actual experience of the partners and their own available technology (seismic modelling and monitoring at NORSAR, S-source and Seabed Logging at NGI, resistivity and extensive field practice at NGU, GPR expertise at UiO, etc).

Figure 1. a), b) GPR equipment (UiO), c) Resistivity equipment (UiO), d) Seismic equipment (UiO)

• To work with students, in order to teach them how to use geophysics, without them needing to be geophysicist, but to give them a sufficient knowledge of the technology to avoid mistakes in the acquisition of the data and interpretation of the results
To work on specific case studies illustrating various aspects of the use of geophysics for geohazards assessment
• To promote publishing at conferences and in peer-reviewed journals within geophysics. It is indeed very important to help gathering experience internationally in order to gain from earlier experiments and to further develop the technology

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Current activities

National and international cooperation

ICG aims at establishing national and international cooperations with relevant partners and projects. Up to now active contacts have been established with

The University of Tromsø, UiT, Norway, gas hydrates.

The Norwegian Defence Research Institute, FFI, Marine Department, geoacoustic.

 The Joseph Fourier University, Grenoble, France, LIRIGM/LGIT, land geophysics.

 The “Ecole et Observatoire des Sciences de la Terre”, EOST, Strasbourg, France.

 The Leibniz Institute for Applied Geosciences, GGA, Hannover, Germany.

 The University of Lund, Sweden, resistivity.

 The University of Århus, Denmark, Geophysics and Geodynamics, resistivity.

 The Moscow State University (MSU), remote sensing and debris flows, Russia.

 Several universities in USA and one in Australia, within a NSF-funded project fpr geohazards.

Contacts exist also with the National Oceanographic Centre, Southampton (NOCS) in offshore geohazards, and with the Swiss Federal Institute of Technology (ETH), Institute of Geophysics, Zürich (glacier and permafrost hazards).

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Past and current activities

State-of-the-Art in Geophysics for Geohazards (land)
Anne-Laure Bouillon, Dipl. Eng. Geophysicist student (University of Strasbourg, France), took her Diploma Thesis at ICG (February-August 2005) in order to:

• use geophysical equipment available at UiO and NGI, and to write simple and well illustrated user-manuals to be used by students, geophysicists and non-geophysicists. Equipments consists mostly of Ground Penetrating Radar (GPR) with several antennas, seismic refraction and reflection acquisition system, and resistivity equipments (systems with electrodes or OhmMapper)
• assist students in field practice: Master students of UiO (Environmental Geology and Geohazards) and other universities (participation to the hydrogeology field course, Bø, Telemark, June 2005, UiO/UMB/HiT cooperation), and
• apply some of the methods to a few test sites for case studies in order to describe the best practice approach in geophysical investigations for geohazard assessment.
• Thesis (ICG report 2005-T1-1) available here (Pdf)

State-of-the-Art in Geophysics for glacial hazards (land)
Isabelle Thollet, Dipl. Eng. Geophysicist student (University of Strasbourg, France), took her Diploma Thesis at ICG (July-December 2006) in order to:

• participate to the planning and execution of geophysical field work at the Flatbre moraine site (see further) on September 2006,
• gather all collected geophysical data at Flatbre and process the seismic ones in order to produce preliminary results at the end of the internship.
• Thesis (ICG report 2006-T1-1) available here (Pdf)

Useful web links and documents for methods overview and best practice:

• Ombeline Méric, Studying landslides with geophysics, PhD. Thesis, University of Grenoble, in French.

• “Association pour la qualité en géophysique appliquée non petrolière”, in French.

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Quick clays, resistivity measurements (land)
Inger Lise Solberg, Ph.D.student, worked at the University of Trondheim (NTNU), in cooperation with ICG, NGU and NVE. Geological conditions and stability related to clay slides were analysed with relationship between clay slide occurrence, stratigraphy, clay composition, geotechnical properties and hydrological conditions. Resistivity measurements were used to map the quick clay distribution. See publication list to access the corresponding Ph.D.Thesis.
This activity is part of the ICG Stability of Soil Slopes project.

Figure 2. Quick clays, Buvika site a) map, b) equipment with electrodes, c) resistivity (figures courtesy of NGU, picture courtesy of Inger-Lise Solberg, NTNU)

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Åknes rock slide
Rock avalanches and related tsunamis represent one of the most serious natural hazards in Norway, and during the last 100 years more than 170 people have lost their lives in western Norway. The Tafjord disaster of 1934 is one major example, where 3.106 m3 rock mass dropped into the fjord generating a major tsunami in the fjord. A similar high risk rockslope failure has been identified at Åknes (Stranda, Møre og Romsdal) and extensive studies of the area have been carried out during summer 2004 and 2005. The estimated volume of unstable rocks is at least 10 times larger than in Tafjord in 1934. ICG is highly involved in the research related to this project, including students, in co-operation with the state-funded Åknes/Tafjord project. Geophysical data are very important for evaluating the geometry and structure of large rockslide failures, which in turn are essential for analyzing stability and the movement pattern.

Figure 3. Case studies. a) and b) Rock slide at Åknes (figures courtesy of NGU), c) Quick clay test site, Sogn Hagekoloni (Oslo), involving students, d) Debris flows, Moraine, Fjærland (pictures from Hedda Breien, UiO)

The Åknes site (Figures 3a and 3b) is a perfect test site for extensive geophysical case studies, extensively carried out by NGU and the Åknes/Tafjord project since 2004. Regarding seismic monitoring, a small system had first been tested summer 2004 at the topmost part of the Åknes slope, with 6 geophones. A subset of the new "Réseau d'Imagerie de Haute Résolution" (IHR), available at Grenoble, which consists of about 300 data channels designed for 3D seismic surveys, was also running from beginning of September 2005 to mid-October 2005. By using the IHR network, both active (seismic imaging using artificial sources with reflection and tomography) and passive (detection of micro-earthquakes indicating fracturing activity and noise analyses to estimate the thickness of the fractured zone) seismic experiments were carried out and the data are under processing and interpretation. Since October 2005, a permanent seismic network of 8 3-C geophones, monitored by NORSAR, is automatically running. Research is on-going in order to study the local seismic activity and later come up with an early-warning system, integrated with other types of measurements.
This activity is part of the ICG Rock Slope failures.

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Monitoring of a railroad line (land)
NGI instrumentation division has developed a monitoring system to detect earth slides encroaching on a railroad line. The monitoring technology is based on the use of geophones. NGI and the Norwegian railway have offered access to and use of the data collected, to be used as input to a case study. The case study is involving a basic evaluation of data (identification of what elements in the data constitutes a slide event), reliability of the determination (elimination of noise not related to sliding), and the criteria to establish alarms responding to the event. Note that the case study does not involve the monitoring system itself, which is controlled by NGI. During summer 2008, a French student (Guillaume Sauvin) acquired additional data to help refine the automatic processing, especially for locating rock falls along the railroad (velocity model, traveltime tables, etc). These data are under analyses.
This activity is part of the ICG Prevention and Mitigation project.

Figure 4. Monitoring system at Rauberget. left) Example of slide signal, right) Example of train signal.

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Flatbre moraine test site (land)
A major debris flow occurred in 2004 in Fjærland (Norway, Sogn og Fjordane) due to the breaking of the Flatbre moraine damming a glacial lake (Figure 3d). The questions to answer now are, for instance, whether the moraine ridge damming the glacial lake is ice cored, partly or fully. It will help to understand if the breaking could be due to significant melting inside the moraine, thus weakening the whole structure. The moraine is about 600 m long in total, about 40 m high and its slope is about 35 degrees. The ridge is approximately 1m wide with a path on top of it. The particles in the moraine range from size of clay to large boulders of several m3.

At the enquiry of fellow researchers studying that case, geophysical field works were carried out in September 2006. Resistivity, GPR and seismic measurements were gathered and are under processing and analysing (Figure 5). Preliminary results can be found in ICG report 2006-T1-1, were presented at two EGU conferences in 2007 (Lima, March, and Vienna, April) and final results can be found in Lecomte et al. (2008). All 3 methods worked very well, which was indeed surprising for the seismics. There is no indication of ice inside the main moraine, only in the smaller and new moraine under formation on the upstream side. Though the whole moraine seems to be much saturated with water (percolation), which explains the good propagation of seismic waves (a sledge hammer was sufficient to acquire very good quality data), its central part seems especially wet. Water is indeed seeping there at the base of the moraine, as seen at summer time. ICG is considering monitoring the moraine, especially to map and follow the waterflow. The 2006 geophysical data may be released for research purposes.
This activity was coordinated with the ICG Slide dynamics project.

Figure 5. Flatbre moraine 2006 field work. a) Resistivity profile across both new (left) and actual moraine (right) showing the clear difference in resistivity between ice and water-saturated moraine material. b) GPR profile on the distal side of the moraine: water-table, layered sediments and bedrock are visible at the base of the moraine. c) Example of a seismic recording on 24-channels for a profile across the moraine.

Glacial hazards in Caucasus, Russia
In the high mountains of Russia, the sub-surface structure of hazard initiation zones is still mainly unconstrained. It may lead to mistakes in glacial hazard assessment. Based on our experience with the Flatbre moraine test side in Norway (see above), we plan to apply and possibly improve geophysical technique for glacial hazard assessment in the Central Russian Caucasus, advance the knowledge of sub-surface structure for terminal, lateral and ablation moraines in the region and revise early-made glacial hazard assessment for key sites, using collected information. Ground Penetrating Radar and Electrical Resistivity Tomography will be applied for the geophysical research during a test field work planned during summer 2009, in cooperation with the Moscow State University. These methods provide best results for debris covered glaciers, buried ice and moraines. Obtained data will be useful for a better understanding of the glacial hazard initiation and so will benefit the international community, especially the populations at glacier risk.

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Subsidence mapped by interferometric Synthetic-Aperture Radar - inSAR (land)
Satellite-based interferometric SAR has proved to be a valuable tool to detect movements of the ground using the Permanent-Scatterers method. NGU is thus mapping successfully the subsidence of the city of Trondheim. ICG/NGU now has a considerable amount of data on movement that needs to be gone through in great detail to isolate unusual behavior. It is easy to create a map showing average velocity and see things that are moving constantly, but many areas move intermittently and this gets hidden in the data. The challenge is to find a method to identify these points within hundreds of thousands of data points. Some preliminary work on developing visualization tools has been done; this work may be continued in cooperation with geostatistics experts abroad. Fieldwork will be performed in Drammen, Åknes, and in Trondheim. The work in Drammen will provide support for the analysis of the existing data covering Drammen. Corner reflectors will be set up at Åknes to test ground-based SAR systems. Finally, resistivity measurements and reflection seismics in Trondheim are considered to obtain additional data for identifying the large movements detected in the Eberg neighborhood. A new effort in the European community (IGOS - geohazards) has also been initiated to work with the application of satellite imaging and radar data for detecting geohazards.
This activity is part of the ICG Prevention and Mitigation project.

Figure 6. inSAR measurements in Drammen (NGU), Norway, with superposition of sediment type (NGI) and subsidence rate, red indicating a reduction in elevation (figure courtesy of John Dehls, NGU)

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Ground interferometric Synthetic Aperture Radar - GinSAR (land)
GinSAR is a portable system that could be deployed at specific locations as needed. In opposition to satellite-based systems (inSAR), GinSAR can provide better resolution, and may be configured to capture horizontal displacements as well as vertical. Satellite-based inSAR provides the capability to monitor large regions and inaccessible areas, but has lower resolutions, cannot capture predominantly horizontal displacements and may not be applicable in areas with very steep slopes. In addition the update frequency of satellite-based inSAR is in the order of months. The goal of the GinSAR project is to develop equipment for measuring from the ground small displacements of rock slopes. GinSAR and inSAR are complementary because inSAR (satellite based) data is not available everywhere, while GinSAR is a portable system that can be deployed at specific locations as needed, possibly after identification from inSAR measurements. Spin off technology from GinSAR is also available, for example for monitoring of clay slopes and snow accumulation for avalanche warning. GinSAR will be tested at the Åknes site (see above). An existing Italian system has been tested there within the Åknes/Tafjord project and the results are very promising. But these tests also highlighted the specific problems encountered when working a fjord.
This activity is part of the ICG Prevention and Mitigation.

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S-wave source for charactization of shallow sediments (offshore)
NGI developed the last years a prototype of S-wave source at sea-bottom for oil and gas exploration. As shear-strength is one of the fundamental geotechnical parameter to constrain for geohazard assessement, there is a clear interest in acquiring more direct S-wave information, otherwise inferred indirectly from primary P-wave reflections. As geotechnical boring is expensive and seldom done for just shallow studies, all new seismic technology capable of providing more S-wave information without a too high cost would be beneficial for offshore geohazards. We are therefore working on designing a smaller version of the actual S-source prototype to be used for shallow structures and operated from a classic research vessel. This activity is of high priority and external funding will be necessary, but preliminary work may be carried out within the following projects (Finneidfjord and Trondheim).
This activity is part of the ICG Offshore Geohazards project and in cooperation with UiT and FFI.

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Finneidfjord, Northern Norway: an ICG field laboratory
NGU has equipment to perform very high-resolution seismic acquisition, combined with detailed seafloor topography. This equipment was used to study the causes of the 1996 Finneidfjord submarine landslide, Norway. In its final extent the slide involved some 1 million cubic meters of ground, of which about 90% was below sea level. Four people died, and several houses, a major section of highway, and a beach were destroyed. A bright reflector was identified on the seismic data and may correspond to free gas collected in relatively sandy layers. The free gas could have contributed to the generation of excess pore pressures and the initiation of the submarine landslide. A US student, Eugene Morgan, is working further with the seismic data in order to extract an estimation of free-gas content and the consequent pore pressure based on amplitude and attenuation analyses. To better relate offshore and onshore structures in a coastal framework, near-surface geophysical methods were applied on land during summer 2007. GPR, resistivity and seismic (refraction tomography and surface waves) gave useful information about an intact site, with probable identification of remaining quick-clay (see reference list). Contacts are taken with the Norwegian Road Authority to possibly ground-proofed some of the identified geological units for calibration of the geophysical results.
This activity is part of the ICG Offshore Geohazards project.

Figure 7. Finneidfjord. a) seafloor rendering and interpretation (Longva et al., 2003), b) VHR seismics with evidence of the bright reflector and gas chimneys (Best et al, 2003).

Trondheim harbour: stability assessment of costal processes.
The Trondheim harbour has been the locus for many large flow slides during the last century (L’Heureux et al., 2007; see reference list). The most recent of these occurred in 1990 just outside the mouth of the Nidelv River and mobilized ca. 5x106 m3 of sediments. The mass movement took place as a liquefaction-induced flow slide outside the river outlet and developed into a lateral spread. The sediment mass slid along a weak layer of loose silty sand recognized by a distinct seismic reflection interpreted from high resolution seismic data acquired offshore by NGU. As the infrastructures of the Trondheim harbour have been progressively built over the fjord, it is very important to check if the geological settings observed offshore on seismic profiles are also present below the onshore part of the harbour. Shear-wave seismic reflection profiles were therefore acquired in the Trondheim harbour in June 2008 by GGA, in cooperation with NGU and ICG and with the financial support of StatoilHydro. The results were beyond all expectations, with a penetration depth larger than 200m, i.e., below bedrock, and very good data quality (Figure 8). The data are under processing and interpretation, and preliminary results were presented at the AGU Fall Meeting in December 2008. These land data will also be part of the Ph.D. Thesis of J.-S. L’Heureux (to be defended early 2009).

This activity is part of the ICG Offshore Geohazards project.

Equipment

Most of the equipment used so far is from the University of Oslo, Department of Geosciences, from NGI and NORSAR. The equipment is provided for free use at ICG (if available) and this gives us a flying start for our "Geophysics for Geohazards" Theme. The equipment covers

• Ground Penetrating Radar (Ramac, Figure 8)
• Resistivity (OhmMapper, Figure 9, and ABEM Terrameter SAS 1000/4000)

In addition, a polarimetric GPR is built at UiO to get benefit of multi-polarisation in a one-run acquisition and will be soon tested.

Figure 10. Resistivity equipment of UiO and its characteristics (OhmMapper only here)

NGU (Trondheim) has also lots of geophysical equipments, extensively used on field in Norway, with

• Ground Penetrating Radar (Pulse EKKO with 50, 100 and 200 MHz antennas)
• Resistivity (Lund Imaging System, electrode spacing 2, 5 and 10 meters)
• Electromagnetics (Geonics EM 31)
• Gravimetry (LaCoste Romberg and Scintrex CG-3 gravity meter)
• Borehole logging (Robertsson Geologging: 500 metres cable, 2 videologger, optical televiewer probe (OPTV), temperature/fluid resisitivity/natural gamma ray probe, resistivity probe (SP, SPR, Short Normal, Long Normal), impellar flowmeter)