Abstract: Relation of Seismicity and Tectonic Provinces, Central Stable Region

S. J. Brocoum, R. H. Goodwin

The central stable region of the United States is subdivided into 21 tectonic provinces using geologic criteria including the presence of basins and arches, structures of macroscopic scale, homogeneity of tectonic structures, and divisions of the central stable region by previous studies. An overlay of all historic earthquakes with MM Intensity >= IV shows a poor correlation with the tectonic provinces. However, the earthquakes clearly are not distributed randomly.

The largest concentration of earthquake epicenters is in the Mississippi embayment which may be the present expression of a Paleozoic aulacogen. Active fault systems extend northeast into the central stable region, and account for the high seismicity of the southern Illinois basin and the eastern Ozark uplift. Another concentration of earthquakes is near Attica, New York (MMI <= VIII-IX), and tentatively are related to the Clarendon-Linden structure. The earthquakes near Calumet, Michigan (MMI <= VII-VIII), are thought to be caused or intensified by mine collapse and may be related to the Keeweenaw fault.

Many earthquakes with MMI <= VII-VIII have occurred near Anna, Ohio. They cannot be related to tectonic structures. Similarly, earthquakes (MMI <= VII) near Manhattan, Kansas, occur on the unfaulted western flank of the Nemaha uplift. Several earthquakes (MMI <= VII) near El Reno, Oklahoma, cannot be related to a tectonic structure. However, these events are on the eastern margin of the Anadarko basin and may be related to reactivated growth faults.

Strain release in the central stable region is not uniform and although some earthquakes can be related to tectonic structures and/or active faults, most cannot. Division of the central stable region into tectonic provinces is a first step in relating seismicity and tectonic structures. In most cases, the basins have been the active tectonic element. Some of the earthquakes may be related to the margins of these subsiding basins, where growth faults have been reactivated.

AAPG Search and Discovery Article #90972©1976 AAPG-SEPM Annual Convention and Exhibition, New Orleans, LA