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source: GeologicalSociety 2017年7月5日
Soluble (karstic) rocks including limestone, gypsum and salt all dissolve underground resulting in cavities and cave systems that may collapse causing sinkholes to form at the surface. Limestone dissolves at a slow rate and is well-known for hosting extensive cave systems.
Gypsum and salt dissolve much faster than limestone and also produce cave systems, but they can evolve on a human timescale rather than a geological one and are seldom seen. As a consequence they pose a geological hazard that can cause sinkholes to develop and rapidly spread. Natural gypsum dissolution has resulted in a severe sinkhole problem affecting the city of Ripon in North Yorkshire, and sinkholes further north such as those at Croft, near Darlington, in County Durham.
These are both places frequented by Lewis Carroll and sinkholes are thought to have inspired the story of Alice in Wonderland. Gypsum dissolution-prone areas can be identified both by the occurrence of sinkholes and the presence of sulphate-rich springs. Salt is highly soluble dissolving in the subsurface to feed saline springs which were called wiches in Medieval times. Consequently, the towns of Droitwich, Northwich and Middlewich are all situated on salt springs.
In these towns salt production utilised the natural springs, then increased brine extraction caused catastrophic subsidence in the surrounding areas. The natural dissolution of soluble rocks continues, but by understanding the controlling mechanisms the worst sinkhole areas can be avoided. In addition, some measures can be put in place to help development in the less sinkhole-prone areas.
source: GeologicalSociety 1:01:49 Early Career Geologist Award 2017 Final (3/5/17) Presentations: • Huw Richards (Early Career Geologist award winner 2017) - Exploring Morocco for Copper & Gold • Tom Critchfield - Hydrothermal Alteration - Implications on a Hydropower Scheme in G... 1:09:00 Inequality in global earthquake risk today_May 2017_London Lecture Description This has already been a shocking century for natural disasters, with over half-a-million people killed in earthquakes in Gujarat (2001), Iran (2003), Sumatra (2004), Pakistan (2005), C... 1:09:29 London Lecture: Space rocks, rockets and robots April 17 Exploring our Solar System today and tomorrow Humans have been fascinated with the night skies since antiquity and have utilised technology to aid in the study of the stars and the planets since t... 1:00:11 London Lecture: Engineering a Dinosaur_March17 Using mechanics and engineering analysis to understand feeding behaviour and skull evolution in dinosaurs and other extinct animals How fossil animals lived, moved and fed has fascinated sci
source: GeologicalSociety 2017年5月26日 Description
This has already been a shocking century for natural disasters, with over half-a-million people killed in earthquakes in Gujarat (2001), Iran (2003), Sumatra (2004), Pakistan (2005), China (2008) and Haiti (2010).
Moreover, in the last few decades several devastating earthquakes have apparently targeted population centres in otherwise sparsely inhabited regions, particularly in Asia. A close examination of this situation reveals that ancient settlements are often located for reasons to do with water supply, access, strategic defence or controlling positions on trade routes, and that these considerations are, in turn often controlled by natural geological phenomena, particularly features of the landscape that are created by earthquakes.
What were originally small villages grow into towns, then cities, and now mega-cities with several million people. But their growth has, in general, not been accompanied by any reduction in exposure to earthquake hazard. It is this close relation between where people live and geology that leads to the apparent bulls-eye targeting of cities by earthquakes. As a result, we should expect many more disasters this century, some of which will be far worse, in terms of mortality, than those we have already seen.
At the same time, earthquakes in the developed world have largely become stories about economic loss, rather than loss of life. An earthquake of moderate-size can kill 40,000 in Iran (at Bam in 2003) but only a handful in California. The question of what to do with the huge populations concentrated in earthquake-prone mega-cities of the developing world is one of the most pressing of our time, and has no easy solution, but there are some inspiring stories and examples from recent earthquakes in Japan, Nepal and even Italy, which suggest ways in which scientists, decision-makers and government can work together to enhance public safety.
Speaker
James Jackson, (Professor of Active Tectonics and former Head of the Department of Earth Sciences in the University of Cambridge)
James was born and raised in India, which established his interest in all aspects of Asia, where much of his research has been concentrated. After a first degree in Geology, he obtained a Ph.D. in Geophysics, using earthquakes to study the processes that produce the major surface features of the continents, such as mountain belts and basins.
In addition to seismology, his current research uses the powerful range of satellite-based techniques now available, combined with observations of the landscape in the field, to study how the continents develop and deform on all scales, from the movement that occurs in individual earthquakes to the evolution of mountain belts. His field work has taken him to many parts of Asia, the Mediterranean, Africa, New Zealand and North America.
He is increasingly involved in how to use the insights obtained by geologists to reduce the appalling risk from earthquakes to populations in developing countries, and currently leads a project called ‘Earthquakes Without Frontiers’ which is a consortium of researchers in UK universities and other institutions, working in partnership with independent earthquake scientists and social scientists in countries throughout the great earthquake belt between Italy and China.
One of its aims is to improve earthquake science and earthquake risk reduction through the exchange of knowledge, information, techniques and data between partner countries.
In 1995 he delivered the Royal Institution/BBC Christmas Lectures on 'Planet Earth: an Explorer's Guide'. He has been elected a Fellow of the Royal Society and the American Geophysical Union, and is also a Fellow of Queens' College, Cambridge.
In 2015 he was awarded a CBE and also the Wollaston Medal of the Geological Society of London. http://www.geolsoc.org.uk/gsllondonle...
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source: GeologicalSociety 2017年3月29日 The fundamental requirements for the entrapment of oil and gas are the presence of a mature source rock, migration of those hydrocarbons from there into a trap, which contains an effective reservoir rock and an appropriate seal. There may be a difference of many millions of years in age of the source, reservoir and seal horizons and the timing of hydrocarbon migration and juxtaposition of these rocks to form a trap is critical. Once formed, many traps may be destroyed or leak, due to later tectonics. When prospects are worked up and assessed, the overall “Chance of Success” is calculated on the basis of the probability of the presence and effectiveness of the source, reservoir and trap. This describes the overall ‘risk’ of finding hydrocarbons within the range estimated and this may vary from 10% in frontier basins to 30—50% in proven basins. There is also ‘uncertainty’, which describes the range of outcomes, even when, say the reservoir rock is found to be present. How thick is it? How porous and permeable? Is the original depositional facies as predicted? How connected is it across the prospect? There is also uncertainty even when hydrocarbons are found, as only a certain amount of appraisal wells can be afforded to establish the range of reserves, before making a multi-billion-dollar decision to develop the field. Above surface uncertainty also exists. The oil and gas business is a capital intensive, long term business. An oil or gas field may have a life of 5 to 50 years, depending on size and economics. There will be uncertainty of future oil price, government tax rates and in some cases, the future political stability of the host country. Environmental sensitivity, community relationships and ‘licence to operate’ are all key aspects which must also be assessed. And of course, the impact of fossil fuels on global warming and climate change, is now also a firm part of the context for any decisions, as the world needs to move to a lower carbon environment.
Speaker: Malcolm Brown, President of the Geological Society After graduating from Kingston Polytechnic (1976), with a BSc in Geology, Malcolm worked in Libya and Saudi Arabia before completing an MSc in Petroleum Geology at Imperial College (1982). He worked at British Gas / BG Group for over 30 years as it evolved from state owned utility to successful international business and was Executive Vice President, Exploration. Malcolm became a Fellow in 1982, served on Council between 2009 and 2012 and became a Chartered Geologist in 2013. He took over as President of the Society in 2016.
