Community resilience to tsunamis along the Southeastern Pacific: a multivariate approach incorporating physical,environmental, and social indicators

Tsunamic events are a frequent hazard to coastal towns. Despite this, the extent to which resilience models can be applied to coastal towns as well as the aspects that should be considered when doing so have not been fully evaluated. There is little information regarding the specific indicators that allow cities to better cope and adapt to the impacts of tsunamis, and this information is especially scarce for developing countries such as Chile. The main objective of this study is to develop a resilience model to explore the extent to which local characteristics influence the resilience of Chilean coastal communities to tsunami hazards. Accordingly, this study presents the Coastal Community Resilience model (The CORE model) for exploring the adaptive capacity of coastal areas affected by tsunamis. This model was then applied to fourteen coastal villages, distributed within four towns, three communes, and two regions of Chile. Data comprising 21 indicators that address the physical, environmental, and social resilience aspects of the villages were obtained on-site and from governmental and municipality databases; these data were then subjected to multivariate analysis in order to determine which indicators most and least affect resilience and whether indicators affect resilience positively or negatively. Variation in resilience among the villages was explained by similarities and differences in the administrative-political, urban, rural, and indigenous characteristics of the study areas. In addition to these results, we discuss land use planning considerations to build community resilience, and we provide insight into the utility of the resilience model proposed here. Overall, our findings shed light on gaps in planning policies and opportunities for planning coastal resilient communities, particularly for those where data of explicit indicators are scarce like in Chile and other developing countries.

     

Nekton variations in tributaries along a hydrologically modified North Carolina estuary

Structure and temporal variability in nekton communities were examined for four small brackish creeks along a major tributary (Adams Creek) of the Neuse River estuary, North Carolina during May–September 1994. An inverse salinity gradient was observed along Adams Creek with highest values in the most upstream creek due to a manmade channel connecting the creek to the Newport River estuary. The nekton communities of the four tributaries were similar with some differences in relative abundance of individual species and timing of recruitment and migrations. Bay anchovies (67%), spot (19%), and brown shrimp (6%) were the most abundant species, with the top ten species accounting for 98% of the total catch. The transport of high salinity water (and presumably nekton larvae) into the headwaters of Adams Creek via the canal appeared to have a strong influence on the nekton community; the nekton community present in the Adams Creek system resembled communities in mesohaline waters closer to the outer banks rather than those in an adjacent creek along the Neuse River estuary (South River estuary). Cluster analysis indicated nekton in the creeks could be grouped into early and late season assemblages. Canonical correspondence analysis suggested that neither the creeks nor the dominant species were strongly related to any measured environmental variables indicating habitat suitability was similar regardless of the differences in watershed activities among the four creeks.     

Theoretical seismogram constraints on some crustal velocity models in the central United States

Summary Earthquake investigations in the central United States require a realistic crustal model for accurate location of seismic events, for the determination of earthquake source parameters, and for theoretical ground motion prediction for an assumed earthquake source. A number of crustal models have been proposed which were based on first arrival refraction data obtained from artificial and natural seismic sources.The reflectivity method for generating realistic theoretical seismograms is used together with recently acquired refraction survey data to distinguish among several of the proposed crustal models. The data used in this study preclude a definitive statement about the nature of the lower crust in the region. However, a crust with two or more layers in the upper 20 km immediately below the basement is preferred. The absence of prominent near yertical reflections suggests that the layers may be separated by rapid velocity gradients rather than by sharp discontinuities.     

Untersuchungen an spilitischen Gesteinen der variskischen Geosynkline in Nordwestdeutschland

21 samples of spilitic rocks of Devonian to Carboniferous age from NW-Germany have been analyzed for major elements, a large group of minor elements and the modal mineral composition. Their major element and mineral composition is comparable to Recent spilites from oceanic ridges. Major emphasis has been given to the absolute and relative abundance of the lanthanides and yttrium. Their pattern, which is most probably not altered during processes of spilitization is that of tholeiitic basalts occuring on the continents and in oceanic islands.Spilitization of the rocks under investigation is explained as a metamorphic process in a partially open system (loss of Si, Ca, and gain of H₂O, CO₂, Na) in a temperature range from 200° to about 400° C. Most abundant new minerals are: albite and chlorite; basaltic relict minerals are: plagioclase (high in Ca) and diopsidic pyroxene. Minerals typical for the temperature range mentioned are: prehnite, pumpellyite, actinolithe, epidote biotite. Microprobe analyses of several typical minerals are listed.

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Unsere Untersuchungen wurden im Rahmen des Sonderforschungsbereichs 48 durchgeführt und die Probenpräparation sowie die Spektrenauswertung aus dessen Mitteln finanziert.

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Wir danken den Herren Dr. Alfred Schneider und Dr. Malte Gramse für die Durchführung der quantitativen Mikrosondenanalysen von zahlreichen Spilitmineralen (Tabelle 6).

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Die Herren Professor D. Meischner und Dr. J. Schneider, Göttingen, unterstützten uns bei der Probenauswahl im Kellerwald. Herr Dozent Dr. S. Meisl (Wiesbaden) überließ uns Proben Pumpellyit-führender Spilite für die Mikrosondenanalyse und das Zentrale Geologische Institut, Berlin, stellte die Probe Mellenbach (Gesteinsstandard BM) zur Verfügung.     

Major,minor, and trace element compositions of peridotitic and basaltic komatiites from the precambrian crust of Southern Africa

Major and trace element compositional data are reported for nine mafic and ultramafic rock samples from the Barberton greenstone belt. Rocks from this province are among the oldest fragments of the Earth's crust (3.5 b.y.). The data are consistent with an oceanic crust related origin for these rocks. The high abundances of Ni in these samples make their origin by fractional crystallization of a primitive magma unlikely but are consistent with their generation by partial melting of an upper mantle source. The basaltic samples from the Komati formation can be related by small degrees of partial melting of a primitive upper mantle source to the peridotitic komatiite which probably derived from much more extensive partial melting of a similar source. REE and especially Ni abundances limit the proportion of olivine that is permitted in the residue.     

Lateral Variations of Lg Coda Q in Southern Mexico

—Broad band digital three-component data recorded at UNM, a GEOSCOPE station, were used to estimate Lg coda Q for 34 medium size (3.9 ≤m _b ≤ 6.3) earthquakes with travel paths laying in different geological provinces of southern Mexico in an effort to establish the possible existence of geological structures acting as wave guides and/or travel paths of low attenuation between the Pacific coast and the Valley of Mexico. The stacked spectral ratio method proposed by XIE and NUTTLI (1988) was chosen for computing the coda Q. The variation range of Q ₀ (Q at 1?Hz) and the frequency dependence parameter η estimates averaged on the frequency interval of 0.5 to 2?Hz for the regions and the three components considered are: i) Guerrero region 173 ≤Q¯ ₀≤ 182 and 0.6 ≤Q¯ ₀ ≤ 0.7, ii) Oaxaca region 183 ≤Q¯ ₀ ≤ 198 and 0.6 ≤Q¯ ₀ ≤ 0.8, iii) Michoacan-Jalisco region 187 ≤Q¯ ₀ ≤ 204 and 0.7 ≤Q¯ ₀ ≤ 0.8 and iv) eastern portion of the Transmexican Volcanic Belt (TMVB) 313 ≤Q ₀≤ 335 and η = 0.9. ¶The results show a very high coda Q for the TMVB as compared to other regions of southern Mexico. This unexpected result is difficult to reconcile with the geophysical characteristics of the TMVB, e.g., low seismicity, high volcanic activity and high heat flow typical of a highly attenuating (low Q) region. Visual inspection of seismograms indicates that for earthquakes with seismic waves traveling along the TMVB, the amplitude decay of Lg coda is anomalously slow as compared to other earthquakes in southern Mexico. Thus, it seems that the high Q value found does not entirely reflect the attenuation characteristics of the TMVB but it is probably contaminated by a wave-guide effect. This phenomenon produces an enhancement in the time duration of the Lg wave trains travelling along this geological structure. This result is important to establish the role played by the transmission medium in the extremely long duration of ground motion observed during the September 19, 1985 Michoacan earthquake. ¶The overall spatial distribution of coda Q values indicates that events with focus in the Michoacan-Jalisco and Oaxaca regions yield slightly higher values than those from Guerrero. This feature is more pronounced for the horizontal component of coda Q. A slight dependence of average coda Q ^?1 on earthquake focal depth is observed in the frequency range of 0.2 to 1.0?Hz approximately on the horizontal component. Deeper (h > 50?km) events yield lower values of Q ^?1 than shallower events. For frequencies higher than 1.0?Hz no clear dependence of Q ^?1 on focal depth is observed. However, due to the estimates uncertainties this result is not clearly established.