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Quaternary tectonic faulting in the Eastern United States 总被引：1，自引：0，他引：1
Russell L. Wheeler 《Engineering Geology》2006,82(3):165-186
Paleoseismological study of geologic features thought to result from Quaternary tectonic faulting can characterize the frequencies and sizes of large prehistoric and historical earthquakes, thereby improving the accuracy and precision of seismic-hazard assessments. Greater accuracy and precision can reduce the likelihood of both underprotection and unnecessary design and construction costs. Published studies proposed Quaternary tectonic faulting at 31 faults, folds, seismic zones, and fields of earthquake-induced liquefaction phenomena in the Appalachian Mountains and Coastal Plain. Of the 31 features, seven are of known origin. Four of the seven have nontectonic origins and the other three features are liquefaction fields caused by moderate to large historical and Holocene earthquakes in coastal South Carolina, including Charleston; the Central Virginia Seismic Zone; and the Newbury, Massachusetts, area. However, the causal faults of the three liquefaction fields remain unclear. Charleston has the highest hazard because of large Holocene earthquakes in that area, but the hazard is highly uncertain because the earthquakes are uncertainly located.Of the 31 features, the remaining 24 are of uncertain origin. They require additional work before they can be clearly attributed either to Quaternary tectonic faulting or to nontectonic causes. Of these 24, 14 features, most of them faults, have little or no published geologic evidence of Quaternary tectonic faulting that could indicate the likely occurrence of earthquakes larger than those observed historically. Three more features of the 24 were suggested to have had Quaternary tectonic faulting, but paleoseismological and other studies of them found no evidence of large prehistoric earthquakes. The final seven features of uncertain origin require further examination because all seven are in or near urban areas. They are the Moodus Seismic Zone (Hartford, Connecticut), Dobbs Ferry fault zone and Mosholu fault (New York City), Lancaster Seismic Zone and the epicenter of the shallow Cacoosing Valley earthquake (Lancaster and Reading, Pennsylvania), Kingston fault (central New Jersey between New York and Philadelphia), and Everona fault-Mountain Run fault zone (Washington, D.C., and Arlington and Alexandria, Virginia). 相似文献
2.
L. I. Gonzalez de Vallejo R. Capote L. Cabrera J. M. Insua J. Acosta 《Marine Geophysical Researches》2003,24(1-2):149-160
A series of clastic dikes and tubular vents were identified in southern Tenerife (Canary Islands). These features are the result of seismic liquefaction of a Holocene sand deposit, as the consequence of a high intensity paleoearthquake. The peak ground acceleration (pga) and magnitude of the paleoearthquake generating these liquefaction features were estimated by back calculation analysis. A representative value of 0.30 ± 0.05 g was obtained for the pga. From this, an earthquake intensity of IX was estimated for the liquefaction site. Magnitude bound methods and energy based approaches were used to determine the magnitude of the paleoearthquake, providing a moment magnitude M = 6.8. The zone in which the liquefaction structures are found has undergone tectonic uplift and is affected by two faults. One of these faults was responsible for displacing Holocene materials. Dating of the uplifted sand formation indicates an age of 10,081 ± 933 years, the liquefaction features ranging from this age to 3490 ± 473 years BP. This paleoearthquake was of much greater magnitude than those known historically. Faults with neotectonic activity are significant features that should be borne in mind when assessing the seismic hazards of the Canary Islands, presently considered as low and mainly of volcanic origin. 相似文献
3.
Evidence of ancient liquefaction-in duced features is presented in the area of the 2003 Zemmouri earthquake (M
w 6.8). This earthquake was related to an offshore unknown 50-km long fault. A 0.55-m coseismic coastal uplift was generated
and extensive liquefaction has been induced in the most susceptible area which correspond to the seaside and along the hydrographic
network, mainly the Sebaou and Isser valley rivers. Field investigations allowed us to identify past liquefaction traces in
the Quaternary deposits. The observed features are represented by sand dikes, sills, and sand vents as well as well-preserved
sand boiled volcanoes. In this work, we also describe the alluvial environment, the hosted localized stratigraphic layer,
the morphology and the geometry of the observed features, as well as the observed deformation (settlement) of the hosted layers
that are among characteristics of the seismically induced features as described in worldwide examples. Our observations represent
a step towards paleoseismological studies in the region knowing that the May 21st 2003 Zemmouri earthquake is produced by
an offshore fault where a direct study of the seismogenic fault is inaccessible. 相似文献
4.
Earthquake induced liquefaction features found in the Karewas of Kashmir Valley are potential tools for estimating energy center, magnitude and peak ground acceleration of the paleoearthquakes. Size, pattern and spatial distribution of liquefaction features and in-situ geotechnical data were collected at the paleoliquefaction sites to assess the magnitude and peak ground acceleration of the paleoearthquake. The magnitude of paleoearthquakes was estimated to be of the order of (Mw = 6.2) using “Magnitude bound method” and “In-situ testing of geotechnical properties and assessment of liquefaction potential of liquefied beds (source stratum) using cyclic stress method”. The peak ground acceleration computed were in the range of 0.27 g to 0.83 g using cyclic stress method and 0.30 g using attenuation equation NDMA [21]. 相似文献
5.
Geotechnical analysis of paleoseismic shaking using liquefaction features: a major updating 总被引：1，自引：0，他引：1
A new methodology is proposed for the geotechnical analysis of strength of paleoseismic shaking using liquefaction effects. The proposed method provides recommendations for selection of both individual and regionally located test sites, provides techniques for validation of field data for use in back-analysis, and presents a recently developed energy-based solution to back-calculate paleoearthquake magnitude and strength of shaking. The proposed method allows investigators to qualitatively assess the influence of post-earthquake density change and aging. The proposed method also describes how the back-calculations from individual sites should be integrated into a regional assessment of paleoseismic parameters. 相似文献
6.
On Tenerife, one of the Canary Islands, a series of clastic dikes and tubular vents is attributed to liquefaction of sediments during a high-intensity paleoearthquake. Geotechnical, geological, tectonic, and mineralogical investigations have been carried out to identify the soil composition and structure, as well as the geological processes operating in the area. Geochronological analysis has indicated an age ranging from 10,081±933 to 3490±473 years BP for the liquefaction features. The area in which these liquefaction features are found has undergone tectonic uplift and is affected by two faults. One of these faults was responsible for displacing the Holocene materials. The paleoearthquake responsible for this liquefaction has been analysed in terms of its peak ground acceleration (pga) and magnitude by back calculation analysis based on the cyclic stress and Ishihara methods. A range of 0.22–0.35g was obtained for the pga, with the value of 0.30g being selected as most representative. From this, an earthquake-modified Mercalli intensity of IMM=IX was estimated for the liquefaction site. The magnitude-bound method and energy-based approaches were used to determine the magnitude of the paleoearthquake, providing a moment magnitude M in the range of 6.4–7.2; M=6.8 is taken as the representative figure. 相似文献
7.
Paleoliquefaction features can be used to estimate lower bounds on the magnitude and ground motion associated with the earthquake that caused the liquefaction feature. The engineering back-analysis of paleoliquefaction features is usually conducted using state of the practice liquefaction-triggering analysis methodologies. Recent studies have shown that these methodologies are associated with variable probabilities of liquefaction depending on the soil parameters. This would imply that estimates of magnitude and ground motion intensity obtained from these methodologies would not be consistent for all soil sites. Moreover, these estimates could be unconservative. In this paper, the use of a probabilistic methodology for the back-analysis of paleoliquefaction features is proposed. The proposed methodology permits the incorporation of model and parameter uncertainty into the analysis and results in more robust estimates of past magnitude and a measure of the uncertainty associated with these predictions. Previously published paleoliquefaction data are used to demonstrate the applicability of the proposed method. Magnitude estimates obtained with the proposed method do not differ significantly from those obtained using deterministic methodologies, but the proposed methodology permits a quantification of the uncertainty associated with magnitude estimates. 相似文献
8.
A series of cone penetration tests (CPTs) were conducted in the vicinity of the New Madrid seismic zone in central USA for quantifying seismic hazards, obtaining geotechnical soil properties, and conducting studies at liquefaction sites related to the 1811–1812 and prehistoric New Madrid earthquakes. The seismic piezocone provides four independent measurements for delineating the stratigraphy, liquefaction potential, and site amplification parameters. At the same location, two independent assessments of soil liquefaction susceptibility can be made using both the normalized tip resistance (qc1N) and shear wave velocity (Vs1). In lieu of traditional deterministic approaches, the CPT data can be processed using probability curves to assess the level and likelihood of future liquefaction occurrence. 相似文献
9.
Discussed in this paper are the factors that control the typical manifestations of liquefaction that are found in continental field settings. The factors are given mainly in terms of the local geologic field situation and the geotechnical properties there. A meaningful interpretation of liquefaction-based data for quantitative analysis of paleoseismic shaking requires understanding of both geologic and geotechnical roles in the mode of ground failure at a specific site.
Recommendations are made for the size of the field area that must be searched for liquefaction effects, in order to develop adequate data for engineering geologic/geotechnical analyses of paleoseismicity. The areal extent must be based on an appreciation that the tectonic situation can cause seismically induced liquefaction effects to form in some locales, but not in others nearby, even for a strong earthquake in the region.
Our guidelines for the conduct of the field search and preliminary analysis of the data relate to three issues for which liquefaction features are especially useful in answering: Has there been strong Holocene/latest Pleistocene shaking in the region? Where was the tectonic source? And what was the strength of shaking? Understanding of the various factors that control the manifestations of liquefaction effects, which we present in this paper, is essential for developing credible answers to these questions. 相似文献
10.
The greatest impediments to the widespread acceptance of back-calculated ground motion characteristics from paleoliquefaction studies typically stem from three uncertainties: (1) the significance of changes in the geotechnical properties of post-liquefied sediments (e.g., “aging” and density changes), (2) the selection of appropriate geotechnical soil indices from individual paleoliquefaction sites, and (3) the methodology for integration of back-calculated results of strength of shaking from individual paleoliquefaction sites into a regional assessment of paleoseismic strength of shaking. Presented herein are two case studies that illustrate the methods outlined by Olson et al. [Engineering Geology, this issue] for addressing these uncertainties.
The first case study is for a site near Memphis, Tennessee, wherein cone penetration test data from side-by-side locations, one of liquefaction and the other of no liquefaction, are used to readily discern that the influence of post-liquefaction “aging” and density changes on the measured in situ soil indices is minimal. In the second case study, 12 sites that are at scattered locations in the Wabash Valley and that exhibit paleoliquefaction features are analyzed. The features are first provisionally attributed to the Vincennes Earthquake, which occurred around 6100 years BP, and are used to illustrate our proposed approach for selecting representative soil indices of the liquefied sediments. These indices are used in back-calculating the strength of shaking at the individual sites, the results from which are then incorporated into a regional assessment of the moment magnitude, M, of the Vincennes Earthquake. The regional assessment validated the provisional assumption that the paleoliquefaction features at the scattered sites were induced by the Vincennes Earthquake, in the main, which was determined to have M7.5. The uncertainties and assumptions used in the assessment are discussed in detail. 相似文献
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