Physical mechanisms in Intraplate earthquakes in United States

Abstract:

 The objective of this study is to investigate the increase in intraplate earthquakes in US and if there is a possible connection with the wells activity. This paper presents a quantitative and qualitative analysis using mid country data records from 1635 to present. Subsequently the search was narrowed to the period from 1965 to 2014 and data from three different catalogues are presented. To satisfy the primary condition for intraplate events we also narrowed the field of our search and took data from the states which were once covered totally or partially by the Great Plains. This area covers approximately ten states totally or partially and has a thicker crust than the rest of the country this parameter is paramount importance on our research.

Next, this paper considered events in the period from 2009 to 2014. Isolating a large midcontinent area we searched for possible links between enhanced earthquakes, geological formation of shale exploited on this period, crustal thickness, and location of cluster quakes. From the results, two events deserved special attention due to their unusual characteristics. Both cases analyzed had the same Magnitude 5.7 and the depth ~5 km (Oklahoma, November) and ~8km (Virginia, August). Both of those events were apparently occurred by the waste water injection wells in each region. Main results indicated as most small and medium earthquakes occurring during the last seven years are strongly related with crustal surface thickness and anthropogenic activity. Though, anthropogenic influence comes from different sources, unconventional wells most associated with waste water injection wells, mining and nuclear explosions.