bluuebunny/crossref_metadata_2025_split huggingface dataset:
Some Observations on the Attenuation of Seismic Waves
Authors: Willis D. E. 
Published: July 2019

Abstract
A number of quarry blasts were recorded on magnetic tape using low frequency seismometers. Spectral analyses were performed on these recordings using variable pass-band filters. Empirical equations involving geometrical spreading plus an appropriate absorption factor were found to fit observed attenuation. Examples are presented showing the effect of various parameters on the spectra of seismic waves generated by these blasts.
A Comparison of Estimates of Seismic Risk in the Central United States
Authors: Howell B. F. 
Published: July 2019

Abstract
Using the maximum likelihood method and a simple least-squares fit relating magnitude and the number of earthquakes per year in the central Mississippi Valley, Nuttli obtained equations which predict that the average recurrence period for a New Madrid-size earthquake is 810 and 980 years, respectively. Using different variants of Gumbel’s theory of extreme events, the average recurrence period is found to be 1100 years (Type I) to 215,000 years (Type III based on recent data only). Conventional methods, including Gumbel’s Type I theory, which make no allowance for an upper limit on the size of expectable earthquakes may overpredict the hazard from earthquakes which are larger than any which have occurred in the historic past.
Bounds on the Average Recurrence Interval of Major Earthquakes Along the Haiyuan Fault In North-Central China
Authors: Peizhen Zhang , Molnar Peter , Weigi Zhang , Qidong Deng , Yipeng Wang , Burchfiel B.C. , Fangmin Song , Royden L. , Decheng Jiao 
Published: July 2019

Abstract
Evidence of surface rupture has been found in trenches near Caiyuan and Shaomayin along the Haiyuan fault, where a great earthquake occurred in 1920. In addition to the 1920 earthquake, faulting occurred at least once between 2590 ± 190 years and 1525 ± 170 years B.P. in Caiyuan, and there probably was another event since 1525 ± 170 years B.P. The formation and later tilting of fault-related, scarp-derived colluvial wedges in the Shaomayin trench appear to record the occurrence of two pre-1920 events in the last 2200–3700 years, but there could have been three or more events. The average recurrence interval for great earthquakes along the Haiyuan fault probably exceeds 700 years, for the 1920 Haiyuan earthquake is the only major event to have been reported in this area in as many years of recorded history. Using a Holocene slip rate along this fault of 8 ± 2 mm/yr, and 8 m as the average amount of offset associated with past great events that have been determined by our previous studies, the resultant earthquake recurrence intervals would be from 800 to 1400 years. The results from our trenches and the historic record are consistent with this range.
Indication of active Faults in the New Madrid Seismic Zone from Precise Location of Hypocenters
Authors: Himes L. , Stauder W. , Herrmann R. B. 
Published: July 2019

Abstract
The hypocenter locations of the larger and better recorded earthquakes of the New Madrid seismic zone are examined in order to determine how closely the hypocenters lie along planar surfaces, thus relating the foci to active fault surfaces. For this purpose more than 500 earthquakes of the region have been selected for study, based on the number (7 or more) of observing stations used in the initial hypocenter location and on the quality of the P-wave onset. These events are relocated using a joint hypocenter-velocity-depth (JHVD) algorithm.
The relocated earthquakes are separated geographically into three trends: ARK, the southwest trending zone from Caruthersville, Missouri, to Marked Tree, Arkansas; DWM, the northeast trending zone from New Madrid to Charleston, Missouri; and CEN, the central, left-stepping offset zone from Ridgely, Tennessee, to New Madrid, Missouri. Vertical profiles taken along and across the ARK and DWM trends verify the strike and dip of dominantly strike slip motion on near vertical active faults along these trends. These results agree with previously determined composite focal mechanism solutions for these trends. No coherent picture has been obtained for the CEN trend.
As a by-product of the study, velocity models from the JHVD inversion are found to be reasonably uniform throughout the New Madrid seismic zone, and to offer supporting evidence for the presence of a shallow low velocity zone in the central portion of the Mississippi embayment.
Seismic Reflection Expression of Reactivated Structures in the New Madrid Rift Complex
Authors: Sexton John. L. 
Published: July 2019

Abstract
An important aspect of seismogenesis concerns the role of preexisting faults and other structural features as preferred zones of weakness in determining the pattern of strain accumulation and seismicity. Reactivation of zones of weakness by present day stress fields may be the cause of many intraplate earthquakes. To understand the relation between reactivated structures and seismicity, it is necessary to identify structures which are properly oriented with respect to the present-day stress field so that reactivation can occur.
The seismic reflection method is very useful for identifying and delineating structures, particularly in areas where the structures are buried as in the New Madrid seismic zone. Application of the seismic reflection method in widely separated locations within the New Madrid rift complex has resulted in successful detection and delineation of reactivated rift-related structures which are believed to be associated with earthquake activity.
The purpose of this paper is to discuss results from seismic reflection profiling in the New Madrid rift complex. Reflection data from several surveys including USGS Vibroseis* surveys in the Reelfoot rift area reveal reactivated faults and other deep rift-related structures which appear to be associated with seismicity. High-resolution explosive and Mini-Sosie** reflection surveys on Reelfoot scarp and through the town of Cottonwood Grove, Tennessee, clearly show reverse faults in Paleozoic and younger rocks which have been reactivated to offset younger rocks. A Vibroseis survey in the Wabash Valley area of the New Madrid rift complex provides direct evidence for a few hundred feet of post-Pennsylvanian age reactivation of large-offset normal faults in Precambrian-age basement rocks. Several earthquake epicenters have been located in the vicinity of these structures. In the Rough Creek graben, Vibroseis reflection data provide clear evidence for reactivation of basement faults.
The success of these reflection surveys shows that well-planned seismic reflection surveys must be included in any program seeking to determine the relationship between preexisting zones of weakness and seismicity of an area.
Aspects of Seismotectonics of Eastern China and their Implications for Eastern U. S.
Authors: Wu Francis T. 
Published: July 2019

Abstract
Earthquakes in eastern China and the eastern United States occur far away from known plate boundaries. M ≥ 8 and 6 < M < 8 events occurred in both areas throughout known history, but the frequency of occurrence of earthquakes was apparently higher in eastern China than in the eastern U.S. Eastern China is composed of many geologically different blocks, which are often bounded by active faults. In comparison the eastern U.S. geology is less heterogeneous. Whereas seismicity in eastern China is frequently, although not always, dearly related to neotectonic activities along the boundaries of “rigid block”, most of the seismogenic structures associated with eastern U.S. events are often overlain by thick recent sediments or have not yet been clearly deciphered; two “rigid blocks” in the eastern U.S. with recognizable seismogenic structures on all sides are tentatively identified. Judging from the episodicity of earthquake occurrence in eastern China in the last 2000 years, we do not yet have enough time to assess the true recurrence rate of earthquakes in the eastern U.S (with a historical record spanning only 400 years). If some eastern U.S. earthquakes occur along boundaries of blocks as they do in eastern China, areas next to the historically active areas in the eastern U.S. may also be sites of significant future seismicity.
The Utility of Geopotential Field Data in Seismotectonic Studies in the Eastern United States
Authors: Hinze William J. , Hildenbrand Thomas G. 
Published: July 2019

Abstract
The deterministic approach to seismic hazard evaluation utilizes all available geologic/geophysical information to map the structure and nature of the crust in three dimensions that may relate to earthquake activity. However, information on the crystalline crust of the eastern United States from direct observations, drilling and sparse crustal seismic studies is limited. In contrast, regional gravity and magnetic anomaly data exist over the entire eastern United States and are available in a digital grid to facilitate processing and analysis. Although these data have serious limitations for detailed interpretation, they can be used to estimate the strength of the crust and the lithosphere and to map and characterize (1) zones of weakness such as paleorifts, sutures, and faults; (2) regions of potential stress amplifications such as plutons and irregularities in fault zones; and (3) basement terranes of generally consistent structural pattern that may delimit coherent regional seismic zones.
Free-air, Bouguer, and isostatic gravity anomalies have different applications in the characterization of the crust for seismogenic purposes and complement magnetic anomaly maps which focus on upper crustal features. In concert, these data have provided the insight to interpret the host structures that together with related seismic and geoscience data, suggest causative mechanisms of the New Madrid seismic zone and other seismogenic regions of the eastern United States. As a result, we conclude that interpretations of geopotential anomalies are an essential ingredient in seismotectonic studies in the eastern United States, but they are only one of several tools required in the concerted effort of assessing seismic hazards. The presence of anomalies with a particular set of attributes neither confirms nor denies the possible spatial relationship to seismicity.
Are Active Mid-Plate Fault Zones of the Central United States Interconnected?
Authors: Slemmons D. B. , Ramelli A. R. 
Published: July 2019

Abstract
It is generally assumed that faults in mid-plate regions, such as central and eastern United States (CEUS), unless historically active, are inactive and/or lack a potential for large earthquakes. The Meers fault in Oklahoma, located in an historically aseismic area, is a spectacular exception to this rule. Paleoseismic studies of this fault show that the most recent large event occurred about 1200 years ago, had a magnitude of more that MS = 7 or 7.5, a surface rupture of 40 km length, and several meters of net displacement on a major left-lateral fault (Ramelli and Slemmons, in press).
At least four fault zones in other parts of CEUS indicate that the Meers faulting event is not unique, including: (1) New Madrid epicentral region with three events of about MS = 8 in 1811 and 1812 with surface faulting and deformation (Russ, 1982), (2) Washita Valley fault (Cox and VanArsdale, 1986), (3) Kentucky River fault (VanArsdale, 1986), and possibly (4) faulting near Pierre, South Dakota (Nichols and Collins, 1987). Moreover, such midplate active faults are not unique, for there are at last four similar examples of historical seismogenic faulting (McCue and others, 1987) with earthquakes of up to 6.9 magnitude.
Most active fault zones can be dearly demonstrated to be parts of branching or interconnected tectonic systems, implying transfer of stress and strain along zones of deformation. We speculate that tectonically active mid-plate fault zones may also be parts of much longer, interconnected active systems, rather than isolated “hot spots” of activity resulting solely from the response of local crustal flaws to a regional stress field.
Structural Control of Seismicity in the Northeastern U. S.
Authors: Seeber L. 
Published: July 2019

Abstract
Seismicity in the northeastern U. S. can often be correlated to preexisting structural features. This correlation is found over a wide range of scales and distinct types of correlation characterize the opposite ends of this range. Firstly, patterns of seismicity measured in tens or hundreds of kms are recognized in maps of recent epicenters from regional networks and in maps of earlier macroseismic epicenters. These patterns are characterized by epicenter bands of resolvable widths, but, within these bands, individual ruptures are often oriented at large angles to the strike of the bands. Several of these seismicity patterns can be spatially correlated to structural features in the crystalline layer of the upper crust which is the source of seismicity. These features are recognized as major lithologic boundaries or suture zones, characterized by ductile deformation without evidence for a subsequent brittle phase. Hence, these large scale features are not preexisting weaknesses reactivated in the current regime. Stress concentration derived from lithologic and rheologic contrast along the boundaries may be an important mechanism in these cases. Secondly, high resolution of aftershock zones in areas where the seismogenic layer outcrops has allowed detailed correlation between ruptures and brittle features. Two cases, one in the Grenville terrane of the craton and the other in the Manhattan Prong along the crystalline core of the Appalachians, show similar characteristics. The ruptures are small, 1.5 and 0.5 kms respectively, but their geometry is well defined by the aftershocks. Both these ruptures are associated with zones of brittle fractures that can be followed at the surface for more than 10 kms. These fracture zones are primarily recognized as topographic lineaments, concentrations of slikensided joints and sets of small en echelon faults. The aftershocks zones are parallel to the individual faults in these en echelon fault sets. The total accumulated horizontal displacement across these fracture zones is small (less than 50 to 100 meters) when compared to the rates of moment release and to the inferred pre-Cenozoic age of these fracture zones. The maximum magnitude from these fracture zones is probably controlled by the size of individual faults in the en echelon pattern, rather than by the much larger dimension of the entire fracture zone.
Establishment of GPS Strain Monitoring Networks in the Eastern United States
Authors: Strange W. E. 
Published: July 2019

Abstract
The National Geodetic Survey (NGS) in cooperation with a number of federal agencies, state and local groups and universities is establishing GPS networks in the United States, east of the Rocky Mountains, which can be used to monitor strain and vertical deformation. These GPS networks are tied to a framework of some 14 fixed and mobile VLBI sites. In cooperation with the Nuclear Regulatory Commission (NRC), NGS established a 45 station GPS regional network in Nov.–Dec. 1987 which is tied to the VLBI framework. This network is scheduled for reobservation in 1989 and funds permitting, at regular intervals thereafter. A number of additional, more dense networks have been or are in the process of being established. The Tennessee Department of Transportation has established a 60 station statewide network to act as a reference network for surveying in conjunction with road construction. This network is expected to have an accuracy of a few parts in 107. NGS in cooperation with the NRC and the University of Maine established in 1986 a high accuracy GPS network in southeast Maine. In 1987 NGS in support of the Federal Aviation Administration (FAA) has established approximately 100 stations throughout Ohio with an accuracy in the 1:106 to 1:107 range. Toward the end of 1988, NGS, working in conjunction with several state agencies and the University of Florida, will establish a statewide network of about 140 stations with an accuracy in the 1:106 to 1:107 range. NGS, in cooperation with the Department of Energy, has also established a high accuracy to 1:107 to 1:108 GPS traverse from Florida to Maine connecting stations at tide gauge sites. The State of Texas is establishing a number of permanent GPS stations in support of highway surveying. These stations will allow strain monitoring across Texas at the 1:108 level. Additional networks are in the planning stage.
It is clear that large numbers of high accuracy GPS networks are being established throughout the eastern United States. Many of these networks are being established for other than geophysical purposes. In many cases the state highway departments and others are interested only in 1:106 accuracy. As a practical matter this means that to assure 1:106 accuracy a few parts in 107 accuracy (1 to 3 cm over 100 kms) is often attained, but this is by no means certain. Also there are normally no plans for systematic resurveys, only replacement of destroyed monuments. A challenge to the geophysical community is to interact with the groups undertaking the high accuracy surveys to assure that, at points of geophysical interest, satisfactory accuracies are achieved during initial epoch measurements. This means that a satisfactory number of observations are obtained and high accuracy reduction methods are used in obtaining differential positions from the data. The geophysical community must also develop plans for resurvey of geophysically interesting network components on a systematic basis.
Seismic History of Minnesota and It’s Geological Significance: An Update
Authors: Chandler Val W. , Morey G. B. 
Published: July 2019

Abstract
High-resolution aeromagnetic data have recently been acquired for most of Minnesota under the sponsorship of the Minnesota Future Resources Commission, which also provided funds for test drilling of selected anomalies. The new data show that northwest-trending dikes and fractures are much more common in the Archean terranes than previously believed, and several epicenters are near such faults. The northeast-trending Great Lakes tectonic zone (GLTZ) was thought to be the chief source of seismicity in the state, because several epicenters were aligned with it. However, more recent seismic reflection profiling has demonstrated that the GLTZ has a moderate dip to the north. This dip is not compatible with the previously favored focal plane solution for a relatively large earthquake, which apparently confirmed the seismogenic role of the GLTZ. The alternative focal plane solution for this earthquake, however, is compatible with some northwest-trending structures in the region.
We propose that the apparent alignment of epicenters with the GLTZ is related to stress buildup at places where it is intersected by northwest-trending faults, with subsequent movement occurring upon release. A similar model may explain seismicity along the northeast-trending Colorado lineament to the southwest.
Estimation Theory for Peak Ground Motion
Authors: Ou Gwo-Bin , Herrmann Robert B. 
Published: July 2019

Abstract
The application of estimation theory for predicting peak ground motion is critically examined in order to be more precise in its application. Estimation theory relates peak ground motion to the duration and spectrum of the signal. Using vertical component data from the Eastern Canada Telemetered Network, at distance range of 100–1000 km, we find that a duration must be defined by the interval where the cumulative energy of the main signal increases linearly, here between 5% and 75% of the cumulative power. This duration, when used with the spectra within this window, adequately replicates observed peak motions. This duration used differs significantly from that used by Herrmann (1985) and Toro and McGuire (1987) beyond 500 km. The estimation theory is extended to estimate confidence limits on the peak motion. Finally, the relation between various spectral level estimators, linear, logarithmic, and RMS, is considered to point out the need for consistency in spectral level estimation using smooth models.
A Student’s Guide to Teleseismic Body Wave Amplitudes
Authors: Okal Emile A. 
Published: July 2019

Abstract
We discuss the nature of the various factors contributing to the amplitude of a teleseismic body wave in the context of a geometrical ray solution, specifically: the radiation of elastic waves into an elastic medium by a point source; the radiation patterns resulting from the orientation of the double-couple in space; the effect of propagation through a radially heterogeneous Earth, known as geometrical spreading; the effect of anelastic attenuation; the contribution of depth phases to the seismogram; and finally the influence of distance on the receiver response function. For each of these parameters, we emphasize the physical arguments underlying the exact algebraic expressions of the various factors contributing to the seismic amplitude. Finally, we discuss the extension of the geometrical ray solution to deep seismic sources.
Real-Time Analog and Digital Data Acquisition Through CUSP
Authors: Peppin William A. , Nicks Walter F. 
Published: July 2019

Abstract
The University of Nevada Seismological Laboratory operates an array of 60 analog short-period and 10 three-component digital telemetered seismic stations, 90 data traces in all, in Nevada and eastern California. Formerly, the seismic data streams were recorded and processed on three separate computers running disparate software and writing incompatible data formats which made access to the digital data quite cumbersome. These systems were recently replaced by a single computer system, a MicroVAX II running VAX/VMS, together with Generic CUSP (Caltech -U.S.G.S. Seismic Processing System), a controlled software system from the U.S.G.S. in Menlo Park. Telemetered digital data are stored simultaneously in two ways, unique to this network. First, these digital data are brought asynchronously into the computer using a standard direct-memory access interface and recorded continuously on an Exabyte 8-mm helical-scan tapedrive. Second, the digital data are passed through a D to A converter and intermixed with the incoming analog data stream used for routine network processing. This analog data stream is then itself digitized and presented to the computer. In this way, calibrated digital waveforms are available in the routine data processing stream, now entirely comprised of digital waveforms, used to locate earthquakes. At the same time, this allows easy access to these data in research applications involving the processing of seismic waveforms.
Structure of the Reelfoot Rift As Interpreted From 2-D Magnetotelluric Models
Authors: Stanley William D. , Rodriguez Brian D. 
Published: July 2019

Abstract
The results of magnetotelluric (MT) surveys reveal structures associated with the Reelfoot rift, including an axial high-resistivity structure that may be related to intrusions in the central part of the rift or to a previously unrecognized horst. The axis of this resistivity high generally follows the central part of the Reelfoot rift, but its orientation is offset several degrees from the enigmatic Blytheville arch. The MT structural high follows the main part of a northeast-trending seismicity belt, but in the New Madrid, Missouri area electrical structures are more complicated. In this northern part of the study area, the strike of resistivity structures determined from the MT data indicate a nearly north-south direction, rather than the N45°E direction indicated for most of the data. If the axial high-resistivity structure represents a horst, then it may form an interior divide between thick shale basins. Faults bounding the proposed horst may be a controlling factor for the northeast trending seismic zone.