Variable rupture mode of the subduction zone along the Ecuador-Colombia coast

Three large earthquakes occurred within the rupture zone of the 1906 Colombia-Ecuador earthquake (M_W = 8.8): in 1942 (M_S = 7.9); 1958 (MS = 7.8); and 1979 (M_S = 7.7). We compared the size and mechanism of these earthquakes by using long-period surface waves, tsunami data, and macroseismic data. The 1979 event is a thrust event with a seismic moment of 2.9 × 10^(28) dyne-cm, and represents subduction of the Nazca plate beneath South America. The rupture length and direction are 230 km and N40°E, respectively. Examination of old seismograms indicates that the 1906 event is also a thrust event which ruptured in the northeast direction. The seismic moment estimated from the tsunami data and the size of the rupture zone is 2 × 10^(29) dyne-cm. The 1942 and 1958 events are much smaller (about 1/5 to 1/10 of the 1979 event in the seismic moment) than the 1979 event. We conclude that the sum of the seismic moments of the 1942, 1958, and 1979 events is only Formula of that of the 1906 event despite the fact that the sequence of the 1942, 1958, and 1979 events ruptured approximately the same segment as the 1906 event. This difference could be explained by an asperity model in which the fault zone is held by a discrete distribution of asperities with weak zones in between. The weak zone normally behaves aseismically, but slips abruptly only when it is driven by failure of the asperities. A small earthquake represents failure of one asperity, and the rupture zone is pinned at both ends by adjacent asperities so that the effective width and the amount of slip are relatively small. A great earthquake represents failure of more than one asperity, and consequently involves much larger width and slip

Velocity contrast across the San Andreas fault in central California: Small-scale variations from P-wave nodal plane distortion

Systematic variations in P-wave radiation patterns, evident in a data set of 400 central California earthquakes, have been analyzed for variations in velocity contrast across the San Andreas fault zone. Vertical strike-slip faulting characterizes the region, with radiation patterns well constrained by the dense local seismographic station network. A discontinuity in crustal velocity occurs across the San Andreas fault. The distribution of systematically inconsistent first motions indicates that first arrivals observed along the fault plane within the northeastern block have followed refracted paths through the higher velocity crustal rocks to the southwest, retaining P-wave polarities characteristic of the quadrant of origin, and thus appearing reversed. A simple geometrical interpretation, with P waves refracted at the fault plane near the focus, yields the velocity contrast across the fault zone; the distribution of hypocenters allows its mapping in time and space. The velocity contrast so determined ranges up to 15 per cent, for a depth range of 1 to 10 km. The observed pattern of contrast values is coherent, with the greatest contrast related apparently in space, and possibly in time, to the larger earthquakes occurring on the fault. We suggest the phenomenon reflects changes in stress state at the fault and, by virtue of its ease of measurement, offers a new and valuable technique in earthquake studies

An inhomogeneous fault model for gaps, asperities, barriers, and seismicity migration

We develop a model for a fault in which various areas of the fault plane have different stress-slip constitutive laws. The model is conceptually simple, involving nonlinear algebraic equations which can easily be solved by a graphical method of successive iterations. Application is made to the problem of explaining seismicity patterns associated with great earthquakes. The model quantitatively explains phenomena associated with seismic gaps, asperities, and barriers

Seismicity near Palmdale, California, and its relation to strain changes

We evaluate the relationships between the spatio-temporal patterns and faulting mechanisms of small earthquakes and the recent temporal changes in horizontal strain observed along the ‘big bend’ portion of the San Andreas fault near Palmdale, California. Microearthquake activity along the entire big bend of the San Andreas fault increased in November 1976 concurrent with the initiation of an earthquake swarm at Juniper Hills. This activity then decreased abruptly to the northwest and southeast of Juniper Hills during the beginning of 1979. This drop in seismic activity occurred around the time that crustal dilatation was observed on the U. S. Geological Survey Palmdale trilateration network. Focal mechanisms from the study region are predominantly thrust. There are two time periods when the mechanisms are closer to strike slip than to thrust. The first period (December 1976 to February 1977) corresponds to the beginning of the Juniper Hills swarm. The second period (November 1978 to April 1979) approximately coincides with a change in trend of the strain data from uniaxial N-S compression to dilatation

Location of earthquake swarm events near Palmdale, California, using a linear gradient velocity model

A series of small earthquakes (0.5 ≦ M_L ≦ 3.0) along a 60-km segment of the San Andreas Fault in the vicinity of Palmdale, California, has been recorded since 1976 by an array operated by the California Institute of Technology. The events were analyzed in two steps. First, travel-time data from four regionally well-recorded events (M_L = 2.2, 2.8, 3.0, 2.8) were inverted using a nonlinear least-squares algorithm to obtain a local velocity model consisting of an upper crustal layer with linearly increasing velocity in dipping contact with a constant velocity half-space. Hypocenters of over 150 events were relocated using this velocity model. Most of the events are clustered between the mapped traces of the San Andreas and Punchbowl faults; however, there has been a migration of activity along the San Andreas Fault. Activity which began in a 5-km cluster has expanded during a 2-yr period to fill a 60-km segment of the fault

Action Planning for Daily Mouth Care in Long-Term Care: The Brushing Up on Mouth Care Project

Research focusing on the introduction of daily mouth care programs for dependent older adults in long-term care has met with limited success. There is a need for greater awareness about the importance of oral health, more education for those providing oral care, and organizational structures that provide policy and administrative support for daily mouth care. The purpose of this paper is to describe the establishment of an oral care action plan for long-term care using an interdisciplinary collaborative approach. Methods. Elements of a program planning cycle that includes assessment, planning, implementation, and evaluation guided this work and are described in this paper. Findings associated with assessment and planning are detailed. Assessment involved exploration of internal and external factors influencing oral care in long-term care and included document review, focus groups and one-on-one interviews with end-users. The planning phase brought care providers, stakeholders, and researchers together to design a set of actions to integrate oral care into the organizational policy and practice of the research settings. Findings. The establishment of a meaningful and productive collaboration was beneficial for developing realistic goals, understanding context and institutional culture, creating actions suitable and applicable for end-users, and laying a foundation for broader networking with relevant stakeholders and health policy makers

Future Seismic Hazards in Southern California - Phase I: Implications of the 1992 Landers Earthquake Sequence

Southern California and its seismologists received a wake-up call on June 28, 1992. The largest earthquake to strike southern California in 40 years occurred near the town of Landers, located 30 km north of the San Andreas fault. It had a magnitude of 7.5 (M7.5). Three and one-half hours later, a M6.5 aftershock struck the Big Bear area 40 km (kilometers) to the west of Landers. An ad hoc working group was rapidly convened in July, 1992, to evaluate how the Landers-Big Bear earthquake sequence might affect future large earthquakes along major faults in southern California. In particular, what are the chances of large earthquakes in the next few years and how do they compare to previous estimates (such as those of the Working Group on California Earthquake Probabilities -- WGCEP, 1988)? Such an evaluation was made for central California after the Lorna Prieta earthquake of 1989 (WGCEP, 1990). The charge to the Landers ad hoc working group included analyzing the seismicity for the last several years in southern California and the new paleoseismic, geologic, and geodetic data recently available for southern California. To inform the public about the potential hazard of plausible earthquakes, the working group was also asked to map the predicted severity of ground shaking for such earthquakes compared to that from the Landers earthquake

Iminosugar-Based Inhibitors of Glucosylceramide Synthase Increase Brain Glycosphingolipids and Survival in a Mouse Model of Sandhoff Disease

The neuropathic glycosphingolipidoses are a subgroup of lysosomal storage disorders for which there are no effective therapies. A potential approach is substrate reduction therapy using inhibitors of glucosylceramide synthase (GCS) to decrease the synthesis of glucosylceramide and related glycosphingolipids that accumulate in the lysosomes. Genz-529468, a blood-brain barrier-permeant iminosugar-based GCS inhibitor, was used to evaluate this concept in a mouse model of Sandhoff disease, which accumulates the glycosphingolipid GM2 in the visceral organs and CNS. As expected, oral administration of the drug inhibited hepatic GM2 accumulation. Paradoxically, in the brain, treatment resulted in a slight increase in GM2 levels and a 20-fold increase in glucosylceramide levels. The increase in brain glucosylceramide levels might be due to concurrent inhibition of the non-lysosomal glucosylceramidase, Gba2. Similar results were observed with NB-DNJ, another iminosugar-based GCS inhibitor. Despite these unanticipated increases in glycosphingolipids in the CNS, treatment nevertheless delayed the loss of motor function and coordination and extended the lifespan of the Sandhoff mice. These results suggest that the CNS benefits observed in the Sandhoff mice might not necessarily be due to substrate reduction therapy but rather to off-target effects

Infection of CD8+CD45RO+ Memory T-Cells by HIV-1 and Their Proliferative Response

CD8+ T-cells are involved in controlling HIV-1 infection by eliminating infected cells and secreting soluble factors that inhibit viral replication. To investigate the mechanism and significance of infection of CD8+ T-cells by HIV-1 in vitro, we examined the susceptibility of these cells and their subsets to infection. CD8+ T-cells supported greater levels of replication with T-cell tropic strains of HIV-1, though viral production was lower than that observed in CD4+ T-cells. CD8+ T-cell infection was found to be productive through ELISA, RT-PCR and flow cytometric analyses. In addition, the CD8+CD45RO+ memory T-cell population supported higher levels of HIV-1 replication than CD8+CD45RA+ naïve T-cells. However, infection of CD8+CD45RO+ T-cells did not affect their proliferative response to the majority of mitogens tested. We conclude, with numerous lines of evidence detecting and measuring infection of CD8+ T-cells and their subsets, that this cellular target and potential reservoir may be central to HIV-1 pathogenesis