Editing Earthquake prediction (section)

==== Dilatancy–diffusion ====
In the 1970s the dilatancy–diffusion hypothesis was highly regarded as providing a physical basis for various phenomena seen as possible earthquake precursors.<ref name=":1">{{Harvnb|Main|Bell|Meredith|Geiger|2012|p=215}}.</ref> It was based on "solid and repeatable evidence"<ref>{{Harvnb|Main|Bell|Meredith|Geiger|2012|p=217}}.</ref> from laboratory experiments that highly stressed crystalline rock experienced a change in volume, or ''dilatancy'',{{efn|1=Subsequent ''diffusion'' of water back into the affected volume of rock is what leads to failure.<ref>{{Harvnb|Main|Bell|Meredith|Geiger|2012|p=215}}; {{Harvnb|Hammond|1973}}.</ref>}} which causes changes in other characteristics, such as seismic velocity and electrical resistivity, and even large-scale uplifts of topography. It was believed this happened in a 'preparatory phase' just prior to the earthquake, and that suitable monitoring could therefore warn of an impending quake.

Detection of variations in the relative velocities of the primary and secondary seismic waves – expressed as Vp/Vs – as they passed through a certain zone was the basis for predicting the 1973 Blue Mountain Lake (NY) and 1974 Riverside (CA) quake.<ref name=":2">{{Harvnb|Hammond|1974}}.</ref> Although these predictions were informal and even trivial, their apparent success was seen as confirmation of both dilatancy and the existence of a preparatory process, leading to what were subsequently called "wildly over-optimistic statements"<ref name=":1"/> that successful earthquake prediction "appears to be on the verge of practical reality."<ref>{{Harvnb|Scholz|Sykes|Aggarwal|1973}}, quoted by {{Harvnb|Hammond|1973}}.</ref>

However, many studies questioned these results,<ref>{{Harvnb|ICEF|2011|pp=333–334}}; {{Harvnb|McEvilly|Johnson|1974}}; {{Harvnb|Lindh|Lockner|Lee|1978}}.</ref> and the hypothesis eventually languished. Subsequent study showed it "failed for several reasons, largely associated with the validity of the assumptions on which it was based", including the assumption that laboratory results can be scaled up to the real world.<ref>{{Harvnb|Main|Bell|Meredith|Geiger|2012|p=226}}.</ref> Another factor was the bias of retrospective selection of criteria.<ref>{{Harvnb|Main|Bell|Meredith|Geiger|2012|pp=220–221, 226}}; see also {{Harvnb|Lindh|Lockner|Lee|1978}}.</ref> Other studies have shown dilatancy to be so negligible that {{Harvnb|Main|Bell|Meredith|Geiger|2012}} concluded: "The concept of a large-scale 'preparation zone' indicating the likely magnitude of a future event, remains as ethereal as the ether that went undetected in the [[Michelson–Morley experiment]]."