Peter Bobrowsky

Summary of Coastal Geologic Evidence for Past Great Earthquakes at the Cascadia Subduction Zone

Earthquakes in the past few thousand years have left signs of land-level change, tsunamis, and shaking along the Pacific coast at the Cascadia subduction zone. Sudden lowering of land accounts for many of the buried marsh and forest soils at estuaries between southern British Columbia and northern California. Sand layers on some of these soils imply that tsunamis were triggered by some of the events that lowered the land. Liquefaction features show that inland shaking accompanied sudden coastal subsidence at the Washington-Oregon border about 300 years ago. The combined evidence for subsidence, tsunamis, and shaking shows that earthquakes of magnitude 8 or larger have occurred on the boundary between the overriding North America plate and the downgoing Juan de Fuca and Gorda plates. Intervals between the earthquakes are poorly known because of uncertainties about the number and ages of the earthquakes. Current estimates for individual intervals at specific coastal sites range from a few centuries to about one thousand years.

Tsunami deposits beneath tidal marshes on Vancouver Island, British Columbia

Thin sheets of sand occur within Holocene mud and peat deposits beneath tidal marshes at Tofino, Ucluelet, and Port Alberni on Vancouver Island, British Columbia. The sand sheets are extensive and have sharp upper and lower contacts. In most cases they consist of moderately sorted, massive sand and silty sand with abundant wood and other plant detritus. At Port Alberni, the thickest sheet has gravel and is graded. The upper two sand sheets in the Tofino-Ucluelet area, and possibly the third, are also present at Port Alberni. Eyewitness accounts and 137 Cs analysis suggest that the uppermost, thinnest sand was deposited by the tsunami triggered by the great Alaska earthquake in 1964. The next oldest sand sheet has been radiocarbon dated at Our data suggest that large tsunamis have struck the southern British Columbia coast several times during the late Holocene and that some were much larger than the 1964 tsunami, which caused about

Tsunamis and tectonic deformation at the northern Cascadia margin: a 3000-year record from Deserted Lake, Vancouver Island, British Columbia, Canada

10 million damage (1964 Canadian dollars) to communities on Vancouver Island. Because such tsunamis can be expected in the future, they pose a hazard to people and property in some coastal areas.

Mapping: Inventories, Susceptibility, Hazard and Risk

Three layers of sand occur within a sequence of muddy gyttja in a 3 m core recovered from Deserted Lake, which lies at the head of a fjord on the central west coast of Vancouver Island, British Columbia, Canada. The sedimentology and microfossil assemblages of these layers are consistent with deposition by tsunamis. Radiocarbon ages suggest that the tsunamis were generated by plate-boundary earthquakes at the Cascadia subduction zone about 2600, 1600 and 300 years ago. Diatom and protozoan contents of the gyttja layers indicate that relative sea level fell in the periods between tsunamis. The sea-level changes are probably a product of interseismic uplift of the North America plate margin. Post-tsunami diatom and protozoan assemblages are generally more marine than their pre-tsunami counterparts, suggesting that the study site subsided during earth quakes. Estimates of interseismic and coseismic deformation during one earthquake cycle indicate that less than half of the interseismic uplift was recovered during the earthquake, leading to cumulative, or permanent, uplift of the area.

Geoheritage and Geoparks in Africa and the Middle-East: Challenges and Perspectives

Generation of landslide maps is of great significance for land use planning, engineering works design and civil protection and risk reduction programmes. Landslide maps may portray past and current landslide occurrence mainly in the form of inventories, zonation of the spatial probability of future landslide occurrence in the form of susceptibility maps, zonation of its spatio-temporal probability in the form of landslide hazard maps, and the expected damage or losses by landslides as risk maps.

Geoheritage, a National Inventory in France

Africa and the Middle East consist of a rich geodiversity, which is regrettably not well known by the public. This is due partly to limited research and studies undertaken in geoheritage and geoconservation in these parts of world, especially those with the intent to explore, inventory and valorize such inherent geodiversity. With the aim to improve this situation, the African Geoparks Network (AGN) was created to increase the awareness of the local population and decision makers regarding the need for sustainable use and management of geoheritage in particular for the benefit of local socio-economic sustainable development targets through the promotion of both geotourism and the creation of unique geoparks.

Fiber Optic Strain Monitoring and Evaluation of a Slow-Moving Landslide Near Ashcroft, British Columbia, Canada

Good protection measures for geological heritage should begin with an inventory of geosites. In France, for example, a law enacted in 2002 grants formal recognition to the notion of geological heritage. An inventory and evaluation were then established on a region-by-region basis. By April 2007, the French Ministry of Environment launched the inventory programme for the nation’s geological heritage and the data are now being collected at a regional scale. The data are being gathered and homogenised, and then transferred to the French National Museum of Natural History for examination. The ratified site data are stored and available for public use on a website (http://inpn.mnhn.fr) in a similar structure to natural data that are also processed and stored (flora, fauna, ecosystems, habitats). Today, protecting global heritage is understood as a dynamic process. Instead of placing objects beneath a display case, the conservation approach is now a more modern, active effort, which facilitates access for knowledge and research.

Multi-parameter Monitoring of a Slow Moving Landslide: Ripley Slide, British Columbia, Canada

Landslides in British Columbia are costly geological hazards that have challenged the major rail companies for over 120 years. Presented here are preliminary results and analyses of fiber Bragg grating and Brillouin optical time domain reflectometry monitoring of a deforming trackside lock-block retaining wall on the Ripley Slide in the Thompson River valley south of Ashcroft, British Columbia. Fiber optic strain data are evaluated in the context of results from global positioning system monitoring, field mapping and electrical resistivity tomographic survey across the landslide. This research aims to reduce the economic, environmental, health and public safety risks that landslides pose to the railway network operating in Canada and elsewhere.

The Landslide Handbook-a Guide to Understanding Landslides: A Landmark Publication for Landslide Education and Preparedness

The Thompson River, south of Ashcroft, British Columbia, Canada is a particularly unique area where complex glacial geology, active geomorphic processes and critical infrastructure (both major national rail lines—CPR and CN) intersect with and are affected by a long history of slope instability. Well documented landslides along a +10 km stretch of the valley have been impacting infrastructure as far back as the 19th century. The Ripley landslide is a small slow moving translational failure that is known to have been active since 1951. It poses a hazard to the onsite infrastructure since both the CN and CPR tracks run adjacent to each other along the entire breadth of the landslide. The economic repercussions of severing both railways here would be pronounced. In response to this threat, an extensive suite of monitoring technology is now being applied that includes: traditional applications including permanent monitoring using GPS stations and piezometers; subsurface investigations involving drilling and shallow seismic surveys; the adoption of novel technologies such as linear fibre optic sensing and vertical subsurface ShapeAccelArray (SAA) inclinometry, the installation of corner reflectors for satellite based (RADARSAT-2) interferometry and the deployment of ground-based SAR and LiDAR for ongoing quantitative assessment. Herein we summarize the collective efforts associated with this extensive array of instrumentation and monitoring studies being undertaken to better manage this and other landslide hazards in Canada and elsewhere.

Canadian Technical Guidelines and Best Practices Related to Landslides: a National Initiative for Loss Reduction

The International Program on Landslides (IPL) aims to conduct international cooperative research and capacity building on landslide risk mitigation, notably in developing countries. To this end, a proposal was submitted to the IPL project committee by landslide researchers from the Geological Survey of Canada and the U.S. Geological Survey. The proposal is entitled IPL 106 “A Best Practices Handbook for Landslide Hazard Mitigation” and was accepted by the ICL/IPL Board of Representatives (BOR) in 2002. As the project evolved, the aim of the Handbook became more comprehensive and the target audience clarified as those charged with emergency management, landslide mitigation, and public education in both developed and developing countries, including those lay persons interested in a comprehensive introduction to Landslide Hazards. The final product and volume entitled “The Landslide Handbook – A Guide to Understanding Landslides” was written by Lynn Highland, U.S. Geological Survey (Landslide Program) and Peter Bobrowsky, Geological Survey of Canada. This handbook is now helping home-owners, community and emergency managers, and decision makers to take the positive step of encouraging awareness of available options and recourse in regard to landslide hazard. As of 2011 The Handbook has been published in four additional languages: Mandarin Chinese, Japanese, Portuguese, and Spanish.