Abstract Problems with and approaches to seismic-hazard estimation in the midcontinent of the United States are evaluated by using recent data on stress regime, crustal age and structure, and seismicity of other stable continental regions. Evaluating earthquake hazard in the central U.S. is difficult because of the lack of identifiable seismogenic faults and because of the low rate of seismic activity. Furthermore, the recurrence intervals of large earthquakes are poorly known, in part because of the short historical record that spans only a fraction of the repeat times of these quakes. The seismotectonic regime of the central U.S. is dominated by the Reelfoot rift complex and the associated New Madrid, Missouri, seismic zone. However, there are other major tectonic structures in the region such as the Nemaha ridge, the Midcontinent rift system, and the Wichita-Ouachita orogenic belt; earthquakes generating damaging ground motion (approximately magnitude 5.0 or greater) have occurred in the states of Ohio, Illinois, Oklahoma, Texas, Kansas, Nebraska, Kentucky, Alabama, and Arkansas, as well as Missouri. Opinions vary widely about the best way to delineate seismic source zones in such a diffuse and varied seismotectonic environment. Moreover, detailed paleoseismic or neo-tectonic data that could improve hazard assessments are extremely sparse in the central United States. The Meers fault scarp in southwestern Oklahoma, with its evidence for Holocene displacement and its lack of background seismicity, highlights a new set of assessment problems. Development of site-specific probabilistic hazard curves are further hampered by the lack of strong ground-motion data and high-resolution attenuation data. We address aspects of the overall seismic-hazard assessment problem for which neotectonic information provides constraints. These include a seismic source zonation for the central U.S. and estimates of maximum possible earthquakes for these zones, especially for the New Madrid region.

Abstract This paper describes the gas pools in the belt of mountain folding comprising the Arbuckle and Wichita Mountains of Oklahoma and the area between and south of these ranges. In that area there are now 22 separate pools which have yielded natural gas and from which gas has been sold in commercial quantity, and 19 oil pools which have produced gas for field use only. All of the gas pools have produced oil also, and in most of them the oil produced has been of much greater value than the gas. In all of the oil fields, casinghead gas from oil wells has been utilized for local power, heat, and light in the fields. Although their gas yield has been overshadowed by the much greater importance of their oil production, these 22 gas pools have sold to outside consumers to January 1, 1932, more than 200 billion cubic feet of gas, for which the producers have received approximately $20,000,000. This is about 5 per cent of the total amount of natural gas produced and sold to that date in Oklahoma, and not quite 1 per cent of the total for the United States. It is believed that at least 100 billion cubic feet of additional gas has been used in the oil and gas fields of southern Oklahoma for local purposes. The known reserves of gas in this area, in sandstones now developed, probably do not exceed 50 billion cubic feet. But this region is believed to contain larger untapped reserves of both gas and oil than any other part of Oklahoma, both in additional pools not yet discovered, and (still more certainly) in deeper sandstones not yet reached, in fields already producing. Although in most of the pools in other parts of the state, the entire sedimentary section, or all of it that is believed to be worth testing, has already been tested by the drill, in many of the pools of southern Oklahoma the surface has hardly been scratched. There is here the thickest sedimentary section (a maximum of 25,000 feet) in the Mid-Continent oil region; and in some of these pools the drill has not yet penetrated one-fourth of the thickness. No test has been drilled deeper than 5,300 feet in any producing area discussed in this paper, and in several pools the deepest test is still far above the base of the Pennsylvanian system, beneath which lie, where the section is complete, 10,000–14,000 feet of older sedimentary rocks. Stratigraphically, the area covered by this paper comprises the western extremity of the Ouachita geosyncline, and was exceptionally active in accumulation of sediments during Ordovician and Pennsylvanian time. Structurally, it differs from the other parts of the Mid-Continent region in having been subjected to close folding. This folding was accomplished in Pennsylvanian time as a part of the orogenic system then extending from Colorado and northern New Mexico southeastward to the Ouachita Mountains or beyond.