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466 • Filth Infernefiona! Symposium on Se~Norfhern Ohio Geo/opice/ Society <br />\ CON =ES`ION <br />~._._90RDER <br />A <br />` kz <br />o <br />2 <br />~~~ <br />'~•. <br />.` ~ ,~ <br />\ `. ~ <br />`. ~ <br />/ ~. <br />~.`•~.~ \ <br />•~ , <br />.\ <br />N \ <br />.~~ gORDEq M <br />v O <br />~ y <br />~\ \ F~~ <br />~` `~pO y~ <br />~,?S ~~ 32s,__ <br />n ~, <br />~ S <br />~ ~ <br />~ ~ <br />~_ _____ I~, ~~ <br />~\ T \ <br />~~ as ~~~ <br />I•y, ~ ~~~ <br />S ~ -- <br />~ ` <br />S~O \\xx `\`~~ <br />~ ~ <br />\ x ~ <br />NCO <br />~HCF <br />~ss,o <br />~ •N <br />~e0 <br />~'PO <br />~R <br />`~ <br />~~ <br />~ ~ <br />~. <br />~\ <br />.\ <br />.\ <br />O O,5 1 1,5 2 KM. ~ <br />[ ~ ~ ~. <br />i' <br />i <br />~' <br />~' <br />~•~ <br />Figure 3. Swcture map on top of the Hengelo sal[ with [he areas of subsidence 1 and 2. <br />There were, however, two great differences, the duration <br />in time of the subsidence and the small area influenced at <br />the surface in relation to the depth of the cavity. As the <br />coalfield practice showed movements at the surface ended <br />after about two years. In the Hengelo case however, the <br />subsidence has lasted for years. At this very moment, after <br />IS years, a vertical displacement of about 5 cm or 2" is still <br />measured in the center of the bowl every year. <br />Unfamiliarity with what actually was happening in the <br />underground made KNZ decide to drill an exploration well <br />between wells 18 and 24 in this area. After the Triassic <br />formation had been reached, great difficulties were encoun- <br />