Soil liquefaction during the Arequipa Mw 8.4, June 23, 2001 earthquake, southern coastal Peru

The Arequipa June 23, 2001, earthquake with a moment magnitude of Mw 8.4 struck southern Peru, northern Chile and western Bolivia. This shallow (29 km deep) interplate event, occurring in the coupled zone of the Nazca subduction next to the southeast of the subducting Nazca ridge, triggered very localized but widely outspread soil liquefaction. Although sand blows and lateral spreading of river banks and road bridge abutments were observed 390 km away from the epicenter in the southeast direction (nearing the town of Tacna, close to the Chile border), liquefaction features were only observed in major river valleys and delta and coastal plains in the meizoseismal area. This was strongly controlled by the aridity along the coastal strip of Southern Peru. From the sand blow distribution along the coastal area, a first relationship of isolated sand blow diameter versus epicentral distance for a single event is ever proposed. The most significant outcome from this liquefaction field reconnaissance is that energy propagation during the main June 23, 2001, event is further supported by the distribution and size of the isolated sand blows in the meizoseismal area. The sand blows are larger to the southeast of the epicenter than its northwestern equivalents. This can be stated in other words as well. The area affected by liquefaction to the northwest is less spread out than to the southeast. Implications of these results in future paleoliquefaction investigations for earthquake magnitude and epicentral determinations are extremely important. In cases of highly asymmetrical distribution of liquefaction features such as this one, where rupture propagation tends to be mono-directional, it can be reliably determined an epicentral distance (between earthquake and liquefaction evidence) and an earthquake magnitude only if the largest sand blow is found. Therefore, magnitude estimation using this uneven liquefaction occurrence will surely lead to underrating if only the shortest side of the meizoseismal area is unluckily studied, which can eventually be the only part exhibiting liquefaction evidence, depending on the earthquake location and the distribution of liquefaction-prone environments.     

An expanding Universe with constant pressure and no cosmological constant

Thanks to its fitting triumph, the ΛCDM paradigm is assumed to be the most powerful model, for describing the Universe dynamics, over much the myriad of cosmological models. Unfortunately, the quest of a self-consistent model remains not well explained, because it is not clear how to solve the problems of fine-tuning and coincidence, afflicting the ΛCDM framework; as a matter of fact, these theoretical drawbacks do not allow to consider the ΛCDM model, as the final picture of the modern cosmological scenario. Here, we show that the simplest model, which provides a constant equation of state for the pressure, leads to a generalization of ΛCDM, reducing to it in a particular case. Moreover, we highlight the physical mechanisms of this model, describing the thermodynamical reasons why a constant pressure should be negative in an expanding Universe. In addition, we fit the free parameters of our model by minimizing the chi square through the age differential method, involving a direct measurement of H.     

Integration schemes with substepping algorithms for creep analysis in geomaterials

This paper describes a robust and efficient methodology for predicting displacements, deformations, and stresses in geomaterials that are susceptible to creep. The methodology is based on two integration schemes, which consider substepping algorithms. The first scheme is used for integrating space-time relations in a global sense, whereas the second scheme is used for integrating stress-stain relations in a local sense. Different from previous studies, both integration schemes are easy to implement and general in the sense that they can be applied to any type of creep law. Through an in-house finite element simulator, several numerical tests are performed. They include triaxial and wellbore closure analyses considering soft soils and salt rocks. The results show that the combination of both schemes leads to stable and accurate solutions with reduced computational time.     

A strong-motion database from the Peru–Chile subduction zone

Earthquake hazard along the Peru–Chile subduction zone is amongst the highest in the world. The development of a database of subduction-zone strong-motion recordings is, therefore, of great importance for ground-motion prediction in this region. Accelerograms recorded by the different networks operators in Peru and Chile have been compiled and processed in a uniform manner, and information on the source parameters of the causative earthquakes, fault-plane geometries and local site conditions at the recording stations has been collected and reviewed to obtain high-quality metadata. The compiled database consists of 98 triaxial ground-motion recordings from 15 subduction-type events with moment magnitudes ranging from 6.3 to 8.4, recorded at 59 different sites in Peru and Chile, between 1966 and 2007. While the database presented in this study is not sufficient for the derivation of a new predictive equation for ground motions from subduction events in the Peru–Chile region, it significantly expands the global database of strong-motion data and associated metadata that can be used in the derivation of predictive equations for subduction environments. Additionally, the compiled database will allow the assessment of existing predictive models for subduction-type events in terms of their suitability for the Peru–Chile region, which directly influences seismic hazard assessment in this region.     

Ground motions observed during the 15 August 2007 Pisco, Peru, earthquake

A M_w 7.9 earthquake event occurred on 15 August 2007 off the coast of central Peru, 60 km west of the city of Pisco. This event is associated with subduction processes at the interface of the Nazca and South American plates, and was characterised by a complex source mechanism involving rupture on two main asperities, with unilateral rupture propagation to the southeast. The rupture process is clearly reflected in the ground motions recorded during this event, which include two separate episodes of strong shaking. The event triggered 18 accelerographic stations; the recordings are examined in terms of their characteristics and compared to the predictions of ground-motion prediction equations for subduction environments, using the maximum-likelihood-based method of Scherbaum et al. (Bull Seismol Soc Am 94(6):2164–2185, 2004). Additionally, macroseismic observations and damage patterns are examined and discussed in the light of local construction practices, drawing on field observations gathered during the post-earthquake reconnaissance missions.     

Phylogeographic patterns in Maguimithrax spinosissimus (Decapoda: Mithracidae) from Colombian Caribbean

The Caribbean king crab Maguimithrax spinosissimus is an important artisanal fisheries resource with a distribution range that includes the Florida Keys and Caribbean Sea islands. We carried out a phylogeographic analysis of M. spinosissimus in one oceanic (Old Providence) and two continental islands (Rosario and Tintipán). We analysed 89 and 49 Control Region (CR) and Cytochrome Oxidase I (COI) sequences, respectively. We found genetic differentiation between Old Providence and Rosario?+?Tintipán units (F_ST values of 0.84 for CR and 0.91 for COI gene), and gene flow between Rosario and Tintipán (F_ST values ?0.0085 for CR, P?>?.88; ?0.01 for COI gene, P?>?.99). Our analysis showed two genetic stocks and possibly an isolated biogeographic unit of M. spinosissimus. We suggest managing the species as different populations, and conducting more ecological and biological studies for the determination of possible cryptic species.     

Mantle derived crystal-poor rhyolitic ignimbrites: Eruptive mechanism from geochemical and geochronological data of the Piedra Parada caldera,Southern Argentina

Trace elements, isotopic modeling and U-Th-Pb SHRIMP zircon age constraints are used to reconstruct the eruption history and magmatic processes of the Piedra Parada Caldera. In the early Eocene, the crystal-poor Barda Colorada ignimbrite(BCI), having 15% micro-porphyritic crystals with respect to magmatic components, erupted a volume estimated in more than 300 km~3. The Piedra Parada caldera is located in the Patagonian Andes foreland, at the southern end of the calderas field of the Pilcaniyeu Volcanic Belt(PVB). This belt is related to an extensional tectonic setting as a result of the collision of the Farallon-Aluk ridge with South America, which enabled the development of a transform ocean/continental plate margin followed by the detachment of the Aluk plate and the opening of a slab window. The BCI extra-caldera Plateau is a 100 m thick deposit, having a lower unit with high silica(Si O_2 76 wt.%),potassium poor rhyolitic composition(trondhjemitic like magma), and an upper unit with normal to high potassium rhyolitic composition(granitic like magma). A trace elements modeling of the BCI units shows that the BCI lower and upper units did not evolve from fractionation or immiscibility in the shallow magma reservoir. The BCI also have a primitive isotopic signature(initial87 Sr/86 Sr =0.7031-0.7049 and ε_(Nd)= +3.4 to +3.65). Thus, tectonic, compositional and isotopic constraints suggest the fast ascent of high silica magmas to a shallow reservoir, and point to an upper mantle origin for these rhyolitic magmas in a transitional(Orogenic-Anorogenic) tectono-magmatic setting. U-Th-Pb SHRIMP zircon crystallization ages of the Syn-caldera stage BCI units(56 -51.5 Ma) show a protracted life of 5 Ma for this caldera reservoir. The age of 52.9 ± 0.3 Ma is considered the best fit for the possible maximum age for the caldera collapse. The Late-caldera magmatism has trachyandesitic and rhyolitic compositions.The trace element modeling suggests that these rhyolites evolve from the trachyandesites and do not evolve from the BCI residual magma. The trachyandesites have U-Th-Pb SHRIMP zircon crystallization ages of 52 ± 1 Ma, suggesting that the caldera eruption was triggered by the arrival of the trachyandesitic magma.     

http://www.sciencedirect.com/science/article/pii/S1674987112001533

The collision of a divergent ocean ridge may evolve into two end cases:in the continuity of ocean-floor subduction.or in the detachment of the subducted plate.The northern Patagonia active plate margin has the unique situation that in Cenozoic time it has been subjected to two divergent ridge collisions,each one representing one of the end members.The Neogene Antarctica-Nazca divergent ridge collision evolved as a continuous ocean-floor subduction system,promoting a magmatic hiatus at the arc axis,the obduction of part of the ridge ocean-floor in the fore-arc.and basaltic volcanism in the back-arc.In contrast,the Paleogene Farallon-Aluk divergent ridge collision evolved into a transform margin,with the detachment and sinking of the Aluk plate and the development of a large slab window.As in the previous case,this collision promoted a magmatic hiatus at the arc axis,but the tectono-magmatic scenario changed to postorogenic synextensional volcanism that spread to the former fore-arc（basalt,andesite,rhyolite） and former back-arc（bimodal ignimbrite flare-up,basalt）.Geochemistry of this slab window synextensional volcanism shows more MORB-like basalts towards the former fore-arc,and MORB-OIB-like basalts towards the former back-arc.Instead,an isolated undeformable crustal block in the former back-arc,with an "epeirogenic" response to the slab window and extensional regime,was covered by OIB-type basalts after uplift.Major elements show that slab window basalts reach TiCh values up to 3 wt%,as compared with the top value of 1.5 wt%of arc magmas.Besides,the MgO with respect to（FeO^t + Al₂O₃） ratio helps to distinguish slab window magma changes from the former fore-arc to the former back-arc and also with respect to the "epeirogenic" block.Higher contents of HFS elements such as Nb and Ta also help to distinguish this slab window from arc magmas and also,to distinguish slab window magma changes from the former fore-arc to the former back-arc and "epeirogenic" block settings.The isotope compositions of slab window magmatism show a disparate coeval array from MORB to crustal sources,interpreted as a consequence of the lack of protracted storage and homogenization due to the extensional setting.     

Late Pleistocene flank collapse of Zempoala volcano (Central Mexico) and the role of fault reactivation

Zempoala is an extinct Pleistocene (∼ 0.7–0.8 Ma) stratovolcano that together with La Corona volcano (∼ 0.9 Ma) forms the southern end of the Sierra de las Cruces volcanic range, Central Mexico. The volcano consists of andesitic and dacitic lava flows and domes, as well as pyroclastic and epiclastic sequences, and has had a complex history with several flank collapses. One of these collapses occurred during the late Pleistocene on the S–SE flank of the volcano and produced the Zempoala debris avalanche deposit. This collapse could have been triggered by the reactivation of two normal fault systems (E–W and NE–SW), although magmatic activity cannot be absolutely excluded. The debris avalanche traveled 60 km to the south, covers an area of 600 km² and has a total volume of 6 km³, with a calculated Heim coefficient (H/L) of 0.03. Based on the textural characteristics of the deposit we recognized three zones: proximal, axial, and lateral distal zone. The proximal zone consists of debris avalanche blocks that develop a hummocky topography; the axial zone corresponds with the main debris avalanche deposit made of large clasts set in a sandy matrix, which transformed to a debris flow in the lateral distal portion. The deposit is heterolithologic in composition, with dacitic and andesitic fragments from the old edifice that decrease in volume as bulking of exotic clasts from the substratum increase. Several cities (Cuernavaca, Jojutla de Juárez, Alpuyeca) with associated industrial, agricultural, and tourism activities have been built on the deposit, which pose in evidence the possible impact in case of a new event with such characteristics, since the area is still tectonically active.     

Most similar neighbor imputation of forest attributes using metrics derived from combined airborne LIDAR and multispectral sensors

In the context of predicting forest attributes using a combination of airborne LIDAR and multispectral (MS) sensors, we suggest the inclusion of normalized difference vegetation index (NDVI) metrics along with the more traditional LIDAR height metrics. Here the data fusion method consists of back-projecting LIDAR returns onto original MS images, avoiding co-registration errors. The prediction method is based on non-parametric imputation (the most similar neighbor). Predictor selection and accuracy assessment include hypothesis tests and over-fitting prevention methods. Results show improvements when using combinations of LIDAR and MS compared to using either of them alone. The MS sensor has little explanatory capacity for forest variables dependent on tree height, already well determined from LIDAR alone. However, there is potential for variables dependent on tree diameters and their density. The combination of LIDAR and MS sensors can be very beneficial for predicting variables describing forests structural heterogeneity, which are best described from synergies between LIDAR heights and NDVI dispersion. Results demonstrate the potential of NDVI metrics to increase prediction accuracy of forest attributes. Their inclusion in the predictor dataset may, however, in a few cases be detrimental to accuracy, and therefore we recommend to carefully assess the possible advantages of data fusion on a case-by-case basis.