Now the Chicago 'blast' is an induced earthquake.
On June 7, 1974, at 19:45:37 GMT, an earthquake of magnitude 3.3 (mb, Nuttli) occurred at Wappingers Falls, New York (41°37.75′N, 73°56.5′W). The maximum intensity was Modified Mercalli V, with a radius of perceptibility of 10 km. This high intensity and rapid fall-off of intensity with distance are presumably associated with a shallow focal depth. Within 10 hr of the event, a portable array of microearthquake recording instruments was installed in the epicentral area. During the following 6-day period, over 100 aftershocks were recorded
As above, this has happened before. Unlike the USGS, these people could throw in some portable seismometers and detect that the first quake was thrust, consistent with the regional high horizontal stress. All of this could have been done for Chicago, but we are contrasting a time with money, to one without.