摘要:

An up‐to‐date global compilation of crustal thickness and Pn velocity values from published seismic refraction and surface wave data has been created. From 297 referenced sources, a total of 2508 crustal thickness and 1806 Pn velocity values have been selected. This represents a significant expansion of previous compilations. The inclusion of surface wave data results in a more uniform coverage of the earth's surface than is possible by using only published refraction data. The crustal thickness data are contoured on a global Van der Grinten projection. This compilation currently resides in a computer data base and is available on computer compatible tape. Recommendations for improvement in form and content will be welcomed, as periodic updates are anticipa

ISSN:0278-7407    

DOI:10.1029/TC001i002p00125

年代:1982

数据来源: WILEY

摘要:

Many major faults, including a large fraction of the San Andreas, appear to be virtually quiescent between great earthquakes. The locked sections of the San Andreas near San Francisco and Los Angeles have little or no seismic activity on the primary fault trace, although secondary faults may be active. Stick‐slip behavior on a fault can be explained in terms of a static coefficient of friction, which is larger than the dynamic or sliding coefficient. In this paper we propose a modification of the friction hypothesis in which chemical lithification (cementation) occurs on the fault between earthquakes. As the stress on the fault increases it becomes large enough to break the cemented bonds between particles causing slip on the fault. We treat this problem quantitatively, assuming that pressure solution is responsible for the cementation. An advantage of this model is that the hydrostatic pressure approaches the lithostatic pressure during cementation so that low fault strengths are predicte

ISSN:0278-7407    

DOI:10.1029/TC001i002p00151

年代:1982

数据来源: WILEY

摘要:

On the Appalachian Plateau of New York, ENE striking joints parallel the mid‐continent contemporary stress field and do not correlate with other structures. Joints within Ohio, Indiana, Michigan, and West Virginia also parallel the mid‐continent maximum horizontal compression as indicated by hydraulic fracture measurements. In northern Indiana, where the contemporary stress field deviates significantly from the orientation of the mid‐continent stress, the attitude of the joints deviates accordingly. In addition to joints, structures on several scales from subcontinent size fracture systems to microfabrics in shales apparently parallel the mid‐continent stress field. From this I conclude that these joints are mode I cracks whose orientation corresponds to the contemporary tectonic stress field. In itself, the formation of these structures constitutes a tectonic event that has often been overlooked in favor of tectonic events that produce the more spectacular but less pervasive faults an

ISSN:0278-7407    

DOI:10.1029/TC001i002p00161

年代:1982

数据来源: WILEY

摘要:

A Permo‐Triassic reconstruction of western Pangea (North America, South America, Africa) is proposed that is characterized by (1) definition of the North Atlantic fit by matching of marginal offsets (fracture zones) along the opposing margins, (2) a South Atlantic fit that is tighter than the BuIlard fit and that is achieved by treating Africa as two plates astride the Benue Trough and related structures during the Cretaceous, (3) complete closure of the Proto‐Atlantic Ocean between North and South America, accomplished by placing the Yucatan block between the Ouachita Mountains and Venezuela, (4) a proposed Hercynian suture zone that separates zones of foreland thrusting from zones of arc‐related magmatic activity; to the northwest of this suture lie the Chortis block and Mexico and most of North America, and to the southeast lie South America, the Yucatan Block, Florida and Africa, and (5) satisfaction of paleomagmatic data from North America, South America, and Africa. Beginning with the proposed reconstruction, the relative motion history of South America with respect of North America is defined by using the finite difference method. Within the framework provided by the proposed relative motion history, an evolutionary model for the development of the Gulf of Mexico and Caribbean region is outlined in a series of 13 plate boundary reconstructions at time intervals from the Jurassic to the present. The model includes (1) formation of the Gulf of Mexico by 140 Ma, (2) Pacific provenance of the Caribbean plate through the North America‐South America gap during Cretaceous time, (3) Paleocene‐Early Eocene back arc spreading origin for the Yucatan Basin, whereby Cuba is the frontal arc and the Nicaragua Rise‐Jamaica‐Southern Hispaniola is the remnant arc, and (4) 1200 km of post‐Eocene cumulative offset along both the Northern and Southern Caribbean Plate Boundary Zones, allowing large‐scale eastward migration of the Caribbean plate with respect to the North and Sout

ISSN:0278-7407    

DOI:10.1029/TC001i002p00179

年代:1982

数据来源: WILEY

摘要:

Recently acquired gravity and aeromagnetic data delineate a large linear gravity anomaly which extends through eastern Kentucky and Tennessee and coincides with a zone of complex, high‐amplitude magnetic anomalies. Basement lithologies in the area can be interpreted as a bimodal volcanic suite which is locally peralkaline in nature. These volcanics appear to be metamorphosed where they lie east of the Grenville front, suggesting they predate the Grenville metamorphic event. The available gravity, aeromagnetic, seismic refraction, and petrologic data, along with regional correlations, suggest that the best tectonic interpretation of these data is that a Keweenawan rift zone extended through the area. This rift can be roughly outlined by the gravity high, which is locally offset, suggesting the presence of transform faults. The boundaries of this rift have been locally reactivated and, in fact, a recent earthquake was located along its western boundary in northern Kentuck

ISSN:0278-7407    

DOI:10.1029/TC001i002p00213

年代:1982

数据来源: WILEY

摘要:

Gravity, magnetic, geologic, and seismicity data have been combined in a seismotectonic analysis of the New Madrid seismic zone. Previous studies have presented evidence for several rift zones in this area (Upper Mississippi embayment), including the Reelfoot rift, a late Precambrian‐early Paleozoic failed arm which extends N‐NE from the ancient continental margin. In this study, we propose that the northern terminus of the Reelfoot rift forms a rift complex which appears to correlate well with the seismicity in the area. This correlation suggests that faults associated with this rift complex are being reactivated in the contemporary stress field (ENE compression). If this interpretation is valid, it represents a seismotectonic model which can be used to predict the extent of future seismicity in the New Madrid seismic zone. The proposed rift complex also provides a coherent model for the tectonic development of this region of the North American midcontin

ISSN:0278-7407    

DOI:10.1029/TC001i002p00225

年代:1982

数据来源: WILEY