Fault structure and mechanics of the Hayward Fault, California, from double-difference earthquake locations

The relationship between small-magnitude seismicity and large-scale crustal faulting along the Hayward Fault, California, is investigated using a double-difference (DD) earthquake location algorithm. We used the DD method to determine high-resolution hypocenter locations of the seismicity that occurred between 1967 and 1998. The DD technique incorporates catalog travel time data and relative P and S wave arrival time measurements from waveform cross correlation to solve for the hypocentral separation between events. The relocated seismicity reveals a narrow, near-vertical fault zone at most locations. This zone follows the Hayward Fault along its northern half and then diverges from it to the east near San Leandro, forming the Mission trend. The relocated seismicity is consistent with the idea that slip from the Calaveras Fault is transferred over the Mission trend onto the northern Hayward Fault. The Mission trend is not clearly associated with any mapped active fault as it continues to the south and joins the Calaveras Fault at Calaveras Reservoir. In some locations, discrete structures adjacent to the main trace are seen, features that were previously hidden in the uncertainty of the network locations. The fine structure of the seismicity suggests that the fault surface on the northern Hayward Fault is curved or that the events occur on several substructures. Near San Leandro, where the more westerly striking trend of the Mission seismicity intersects with the surface trace of the (aseismic) southern Hayward Fault, the seismicity remains diffuse after relocation, with strong variation in focal mechanisms between adjacent events indicating a highly fractured zone of deformation. The seismicity is highly organized in space, especially on the northern Hayward Fault, where it forms horizontal, slip-parallel streaks of hypocenters of only a few tens of meters width, bounded by areas almost absent of seismic activity. During the interval from 1984 to 1998, when digital waveforms are available, we find that fewer than 6.5% of the earthquakes can be classified as repeating earthquakes, events that rupture the same fault patch more than one time. These most commonly are located in the shallow creeping part of the fault, or within the streaks at greater depth. The slow repeat rate of 2–3 times within the 15-year observation period for events with magnitudes around M = 1.5 is indicative of a low slip rate or a high stress drop. The absence of microearthquakes over large, contiguous areas of the northern Hayward Fault plane in the depth interval from ∼5 to 10 km and the concentrations of seismicity at these depths suggest that the aseismic regions are either locked or retarded and are storing strain energy for release in future large-magnitude earthquakes

Seismotectonics of the San Andreas Fault System Between Point Arena and Cape Mendocino in Northern California\u27 Implications for the Development and Evolution of a Young Transform

The northernmost and relatively youthful segment of the San Andreas fault system is situated within a 100+ km wide zone of northwest trending strike-slip faults that includes, from west to east, the San Andreas, Maacama, and Bartlett Springs faults. Although the San Andreas fault is the principal strike-slip fault in this system, it has been virtually aseismic since the 1906 earthquake. Moderate levels of seismicity locate to the east along the Maacama fault and, to a lesser extent, the Bartlett Springs fault at focal depths typical of other strike-slip faults within the San Andreas fault system in central California. North of the San Andreas fault system, within the Cape Mendocino area, earthquakes occur at depths of up to 40 km and primarily reflect internal deformation of the subducting Garda slab, and slip along the Mendocino Fracture Zone. Seismicity along the Maacama and Bartlett Springs faults is dominated by right-lateral to oblique-reverse slip along fault planes that dip 50 °-75 ° to the northeast. The northern extent of seismicity along these faults terminates near the surface projection of the southern edge of the Garda slab. The onset of seismicity along these faults may be related to the abrupt change in the elastic thickness of the North American plate as it enters the asthenaspheric window. The Maacama and Bartlett Springs faults are strike-parallel with active reverse faults within the forearc region of the Cascadia subductian zone. This preexisting structural fabric of northwest trending reverse faults in the forearc area appears to have strongly influenced the initial slip and complexity of these faults. Continuation of the moderately dipping Maacama fault to the southeast along the steeply dipping Healdsburg and Rodgers Creek fault zones and the near-vertical Hayward and Calaveras fault zones in the San Francisco Bay area suggests that these faults evolve toward a more vertical dip to minimize the shear stresses that tend to resist plate motion

Austria-Hungary in British public opinion 1866-1918.

Thesis ()--Boston UniversityAustria-Hungary was the first major power to be destroyed by nationalism which triumphed in Europe between the two World Wars and now appears as determining force in Asia and Africa. Today friction among ethnic groups in all parts of the world, financial burdens resulting from military preparedness, threats of Russian expansion, and the obstacles to any political or economic European union renew interest in similar difficulties which confronted the Habsburg Empire. Great Britain's reaction to conditions in Austria-Hungary vividly illustrates the multiplicity of factors in public opinion--the constant struggle between emotion and considered judgment as well as the importance of basic cultural, religious, and political beliefs which color all ideas and attitudes

Three-dimensional structure of the crust and mantle beneath the island of Hawaii.

Thesis. 1978. Ph.D.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Sciences.Microfiche copy available in Archives and Science.Vita.Bibliography : leaves 263-277.Ph.D

Generation of Thymidine Kinase-Deficient Mutants of Infectious Laryngotracheitis Virus

AbstractCurrent vaccines for the avian respiratory disease infectious laryngotracheitis consist of naturally attenuated strains of the causative agent—the herpesvirus infectious laryngotracheitis virus (ILTV). Due to the dissemination of these viruses from vaccinated chickens as well as their possible reversion to more pathogenic forms, the use of genetically engineered viral vaccines lacking virulence factors while retaining antigenicity is being considered. Since the thymidine kinase (TK) activity of herpesviruses has been associated with virulence, inactivation of the encoding gene in the ILTV genome should attenuate the virus. Moreover, by analogy to other TK- herpesviruses, the ability of such ILTV mutants to induce a protective response in chickens should not be compromised. Therefore, the deliberate genetic alteration of ILTV was attempted. In order to prevent reversion and also to enable identification of the modified virus, a "marker" transcriptional unit (Escherichia coli lacZ gene fused to a SV-40 3′-polyadenylation signal sequence and regulated by the pseudorabies virus gX gene promoter) was inserted via homologous recombination at one of two loci within the ILTV TK gene. Recombinant viruses were identified and plaque-purified on the basis of their ability to produce β-galactosidase. Retention of the foreign DNA at the predicted sites in the genomes of the recombinant ILTV was verified by Southern hybridization. Since their replication was unaffected by the thymine analog 1-(2-fluoro-2-deoxy-β-d-arabinofuranosyl)-5-methyluracil, the recombinants appeared to have a TK- phenotype. Despite this apparent deficiency, prior inoculation of either recombinant virus into chickens afforded the birds protection against a lethal challenge of virulent ILTV. Moreover, the degree of respiratory distress in the chickens vaccinated with the recombinants was relatively mild compared to the severe reaction in birds receiving the parental virus. Thus, ILTV can be genetically attenuated without an accompanying loss of immunogenicity

Natural selection favoring more transmissible HIV detected in United States molecular transmission network.

HIV molecular epidemiology can identify clusters of individuals with elevated rates of HIV transmission. These variable transmission rates are primarily driven by host risk behavior; however, the effect of viral traits on variable transmission rates is poorly understood. Viral load, the concentration of HIV in blood, is a heritable viral trait that influences HIV infectiousness and disease progression. Here, we reconstruct HIV genetic transmission clusters using data from the United States National HIV Surveillance System and report that viruses in clusters, inferred to be frequently transmitted, have higher viral loads at diagnosis. Further, viral load is higher in people in larger clusters and with increased network connectivity, suggesting that HIV in the United States is experiencing natural selection to be more infectious and virulent. We also observe a concurrent increase in viral load at diagnosis over the last decade. This evolutionary trajectory may be slowed by prevention strategies prioritized toward rapidly growing transmission clusters