The Southern Region of Peru Earthquake of June 23rd, 2001

The western border of South America is one of the most important seismogenic regions in the world. In this region the most damaging earthquake ever recorded occurred. In June 23rd, 2001, another very strong earthquake (Mw = 8.1–8.2) occurred and produced death and damages in the whole southern region of Peru. This earthquake was originated by a friction process between Nazca and South American plates and affected an area of about 300 km × 120 km defined by the distribution of more than 220 aftershocks recorded by a local seismic network that operated 20 days. The epicenter of the main shock was localized in the northwestern extremity of the aftershock area, which suggests that the rupture propagated towards the SE direction. The modeling of P-wave for teleseismic distances permitted to define a focal mechanism of reverse type with NW-SE oriented nodal planes and a possible fault plane moving beneath almost horizontally in NE direction. The source time function (STF) suggests a complex process of rupture during 85 sec with 2 successive sources. The second one of greater size, and located approximately 100–120 km toward the SE direction was estimated to have a rupture velocity of about 2 km/sec on a 28°-dipping plane to the SE (N135°). A second event happened 45 sec after the first one with an epicenter 130km farther to the SE and a complex STF. This event and the second source of the main shock caused a Tsunami with waves from 7 to 8 meters that propagated almost orthogonally to the coast line, by affecting mainly the Camaná area.Three of all the aftershocks presented magnitudes greater or equal to Mw = 6.6, two of them occurred in front of the cities of Ilo and Mollendo (June 26th and July 7th) with focal mechanisms similar to the main seismic event. The aftershock of July 5th shows a normal mechanism at a depth of 75 km, and is therefore most likely located within the subducting Nazca plate and not in the coupling. The aftershocks of June 26th (Mw = 6.6) and July 5th (Mw = 6.6) show simple short duration STF. The aftershock of July 7th (Mw = 7.5) with 27-second duration suggests a complex process of energy release with the possible occurrence of a secondary shock with lower focal depth and focal mechanism of inverse type with a great lateral component. Simple and composed focal mechanisms were elaborated for the aftershocks and all have similar characteristics to the main earthquake.The earthquake of June 23rd caused major damages in the whole southern Peru. The damage in towns of Arequipa, Moquegua allow to consider maximum intensities from 6 to 7 (MSK79). In Alto de la Alianza and Ciudad Nueva zones from Tacna, the maximum intensity was of 7⁻ (MSK79).     

A fossil aardvark (Mammalia, Tubulidentata) from the lower Pliocene of Chad

The Mission Paléoanthropologique Franco-Tchadienne (MPFT) found a new species of Orycteropodidae (Mammalia, Tubulidentata) in the Kollé fossiliferous sector, northern Chad. After Orycteropus abundulafus [Journal of Vertebrate Paleontology 20 (1) (2000) 205–209; Lehmann, T., Vignaud, P., Likius A., Brunet M., in press. A new Orycteropodidae (Mammalia, Tubulidentata) in the Mio-Pliocene of Northern Chad. Zool. J. Linnean Soc.], this specimen is the second complete skeleton of fossil aardvark found in the Djurab desert. It is the first complete representative of an Orycteropus species found in the Pliocene of Africa. In regard to the Miocene fossil aardvarks, this new taxon, Orycteropus djourabensis nov. sp., shows more affinities with the extant O. afer. The main differences are the larger teeth and the shorter hand in the fossil form. Kossom Bougoudi and Kollé represent a chronological series that gives a unique opportunity for studying the evolution of the African Tubulidentata around the Mio-Pliocene boundary (5.5-4 My). The new species is distinct from the older Chadian Orycteropodid from KB and it embodies the taxonomic turnover that took place within the order Tubulidentata around this boundary in Africa. Moreover, this new species is the oldest known Orycteropus species that clearly belongs to the modern forms including the extant aardvark.     

Controls by saturation state on etch pit formation during calcite dissolution

Dissolution experiments were conducted on {101?4} cleavage faces of calcite at various under-saturations to determine how the saturation state controls etch pit formation. Experimental observations were made by using in situ fluid cell Atomic Force Microscopy. Three dissolution modes were observed. When the saturation index Ω > 0.541, no etch pit formation was seen and dissolution primarily occurred at existing steps. When Ω decreased to Ω_c = 0.541-0.410, the first visible pits appeared and continuous reduction in saturation state slowly increased the pit density on terraces while dissolution simultaneously proceeded at step edges. Finally, when the saturation state fell below Ω_max = ∼0.007, a precipitous increase in pit density took place that sharply contrasted to the ordered fashion of pit formation observed at saturation conditions above this level. These observations are interpreted to be two-dimensional and unassisted pit formation at Ω < ∼0.007, defect- and step-assisted dissolution in between Ω = 0.541 and 0.007, and existing step-induced dissolution for Ω > 0.541.The values of Ω_c are in good agreement with the dislocation theory's predicted critical under-saturations for pit formation at line dislocations. The occurrence of Ω_max is not directly predicted but is a logical consequence of dissolution thermodynamics. These findings suggest that (1) dissolution near and far from equilibrium (i.e., Ω > Ω_c, Ω < Ω_max) is not controlled by dislocations, therefore (2) dislocation density should significantly impact dissolution rate only in the saturation range of Ω_max < Ω < Ω_c; (3) dissolution kinetics and chemical affinity of dissolution reactions should have a non-linear relationship: at sufficiently close to equilibrium, when dislocations cannot open up to form etch pits, the dissolution kinetics will be limited by the number of existing steps; at far from equilibrium, when pits are able to form in defect-free regions, the dissolution rate will be capped by the maximum number of achievable steps.These findings may provide explanations for several well-observed geochemical relationships, including the weak dependence of dissolution rate upon dislocation density in distilled water and the ‘plateau’ behavior of dissolution kinetics both near and far from equilibrium. The explosive occurrence of unassisted pit nucleation at Ω ∼ Ω_max is not predicted by the current dissolution rate equations. This suggests that an accurate ‘general’ rate law describing universal dissolution processes has yet to be developed.     

Calculation of strongly singular and hypersingular surface integrals

Efficient numerical computation of integrals defined on closed surfaces in ℝ³ with non-integrable point singularities that arise in physical geodesy is discussed. The method is based on the use of polar coordinates and the definition of integrals with non-integrable point singularities as Hadamard finite part integrals. First the behavior of singular integrals under smooth parameter transformations is studied, and then it is shown how they can be reduced to absolutely integrable functions over domains in ℝ². The correction terms that usually arise if the substitution rule is formally applied, in contrast to absolutely integrable functions, are calculated. It is shown how to compute the regularized integrals efficiently, and, numerical efforts for various orders of singularity are compared. Finally, efficient numerical integration methods are discussed for integrals of functions that are defined as singular integrals, a task that typically arises in Galerkin boundary element methods. Received: 15 April 1997 / Accepted: 7 May 1998     

Deglacial to middle Holocene (16,600 to 6000 calendar years BP) climate change in the northeastern United States inferred from multi-proxy stable isotope data, Seneca Lake, New York

Climate change in the northeastern United States has been inferred for the last deglaciation to middle Holocene (∼16,600 to 6000 calendar years ago) using multi-proxy data (total organic matter, total carbonate content, δ¹⁸ O calcite and δ¹³ C calcite) from a 5 m long sediment core from Seneca Lake, New York. Much of the regional postglacial warming occurred during the well-known Bolling and Allerod warm periods (∼14.5 to 13.0 ka), but climate amelioration in the northeastern United States preceded that in Greenland by ∼2000 years. An Oldest Dryas climate event (∼15.1 to 14.7 ka) is recognized in Seneca Lake as is a brief Older Dryas (∼14.1 ka) cold event. This latter cold event correlates with the regional expansion of glacial Lake Iroquois and global meltwater pulse IA. An increase in winter precipitation and a shorter growing season likely characterized the northeastern United States at this time. The Intra-Allerod Cold Period (∼13.2 ka) is also evident supporting an “Amphi-Atlantic Oscillation” at this time. The well-known Younger Dryas cold interval occurred in the northeastern United States between 12.9 and 11.6 ka, consistent with ice core data from Greenland. In the Seneca Lake record, however, the Younger Dryas appears as an asymmetric event characterized by an abrupt, high-amplitude beginning followed by a more gradual recovery. Compared to European records, the Younger Dryas in the northeastern United States was a relatively low-amplitude event. The largest amplitude and longest duration anomaly in the Seneca Lake record occurs after the Younger Dryas, between ∼11.6 and 10.3 ka. This “post-Younger Dryas climate interval” represents the last deglacial climate event prior to the start of the Holocene in the northeastern United States, but has not been recognized in Greenland or Europe. The early to middle Holocene in the northeastern United States was characterized by low-amplitude climate variability. A general warming trend during the Holocene Hypsithermal peaked at ∼9 ka coincident with maximum summer insolation controlled by orbital parameters. Millennial- to century-scale variability is also evident in the Holocene Seneca Lake record, including the well-known 8.2 ka cold event (as well as events at ∼7.1 and 6.6 ka). Hemispherical cooling during the Holocene Neoglacial in the northeastern United States began ∼5.5 ka in response to decreasing summer insolation.     

D/H ratios in speleothem fluid inclusions: A guide to variations in the isotopic composition of meteoric precipitation?

D/H ratios of fluid inclusion waters extracted from²³⁰Th/²³⁴U-dated speleothems that were originally deposited under conditions of isotopic equilibrium should provide a direct estimate of the hydrogen isotopic composition of ancient meteoric waters. We present here D/H ratios for 47 fluid inclusion samples from thirteen speleothems deposited over the past 250,000 years at cave sites in Iowa, West Virginia, Kentucky and Missouri. At each site glacial-age waters are depleted in deuterium relative to those of interglacial age. The average interglacial/glacial shift in the hydrogen isotopic composition of meteoric precipitation over ice-free areas of east-central North America is estimated to be ?12‰. This shift is consistent with the present climatic models and can be explained in terms of the prevailing pattern of atmospheric circulation and an increased ocean-continent temperature gradient during glacial times which more than compensated for the increase in deuterium content of the world ocean.     

Feeding rates of the sea nettle,Chrysaora quinquecirrha,under laboratory conditions

The scyphomedusa, Chrysaora quinquecirrha, preys on a variety of estuarine organisms. A series of experiments were conducted to measure the feeding rate of adult medusae on zooplankton prey. Artemia was used as a substitute for the endemic and abundant copepod, Acartia tonsa. The feeding rates ranged from three Artemia per hour per ml of medusae volume to 107 per hour per ml in 51 trials. The consumption was also linearly related to the initial prey concentration. Certain results suggested that a toxic factor might be exuded by the medusae, affecting the observed feeding rates. The results verify the possibility that Acartia may be a major prey organism in estuarine environments.     

On the significance and utilization of secondary magnetizations in red beds

We document three cases of observed Quaternary or much older secondary magnetizations in red beds. A better than usual knowledge about past and present temperature conditions enables us to compare these secondary magnetizations with theoretical relationships between relaxation time and the temperature of acquisition of viscous partial thermo remanent magnetizations (VpTRM's). Arguments can be made for a viscous-thermal origin of the secondary magnetizations in two of the red bed collections, involving Beltian argillites from Montana and Late Precambrian red beds from the Michigan basin. In the third cases, involving Upper Keweenawan sediments from the Upper Peninsula of Michigan, a chemical origin must be assigned to the secondary magnetizations, because thermal and viscous cuases can be ruled out. Stability, blocking-temperature ranges, and discreteness of secondary and characteristics magnetizations are very similar for all three of the red bed collections, so that apparently no magnetic criteria exist to distinguish between partial remagnetizations of thermal or chemical origin in red beds. However, when thermal causes can be documented the theory of VpTRM acquisition offers possibilities for palaeo-heat-flow determinations.