How to fill the biodiversity data gap:Is it better to invest in fieldwork or curation?

Data gaps and biases are two important issues that affect the quality of biodiversity information and downstream results.Understanding how best to fill existing gaps and account for biases is necessary to improve our current information most effectively.Two current main approaches for obtaining and improving data include(1)curation of biological collections,and(2)fieldwork.However,the comparative effectiveness of these approaches in improving biodiversity data remains little explored.We used the Flora de Bogota project to study the magnitude of change in species richness,spatial coverage,and sample coverage of plant records based on curation versus fieldwork.The process of curation resulted in a decrease in species richness(synonym and error removal),but it significantly increased the number of records per species.Fieldwork contributed to a slight increase in species richness,via accumulation of new records.Additionally,curation led to increases in spatial coverage,species observed by locality,the number of plant records by species,and localities by species compared to fieldwork.Overall,curationwas more efficient in producing new information compared to fieldwork,mainly because of the large number of records available in herbaria.We recommend intensive curatorial work as the first step in increasing biodiversity data quality and quantity,to identify bias and gaps at the regional scale that can then be targeted with fieldwork.The stepwise strategy would enable fieldwork to be planned more costeffectively given the limited resources for biodiversity exploration and characterization.

Depth to the bottom of magnetic layer in South America and its relationship to Curie isotherm,Moho depth and seismicity behavior

We have estimated the DBML（depth to the bottom of the magnetic layer） in South America from the inversion of magnetic anomaly data extracted from the EMAG2 grid. The results show that the DBML values, interpreted as the Curie isotherm, vary between -10 and -60 km. The deepest values（〉-45） are mainly observed forming two anomalous zones in the central part of the Andes Cordillera. To the east of the Andes, in most of the stable cratonic area of South America, intermediate values（between -25 and-45 km） are predominant. The shallowest values（〈-25 km） are present in northwestern corner of South America, southern Patagonia, and in a few sectors to the east of the Andes Cordillera. Based on these results, we estimated the heat flow variations along the study area and found a very good correlation with the DBML. Also striking is the observation that the thermal anomalies of low heat flow are closely related to segments of flat subduction, where the presence of a cold and thick subducting oceanic slab beneath the continent, with a virtual absence of hot mantle wedge, leads to a decrease in the heat transfer from the deeper parts of the system.After comparing our results with the Moho depths reported by other authors, we have found that the Curie isotherm is deeper than Moho in most of the South American Platform（northward to -20°S）, which is located in the stable cratonic area at the east of the Andes. This is evidence that the lithospheric mantle here is magnetic and contributes to the long wavelength magnetic signal. Also, our results support the hypothesis that the Curie isotherm may be acting as a boundary above which most of the crustal seismicity is concentrated. Below this boundary the occurrence of seismic events decreases dramatically.

Establishing geothermometric constraints on the local geothermal gradients:Case study of the Eastern Cordillera Basin,Colombia

Geochemical analyses were performed on 170 coal bed-trapped groundwater samples from 97 underground mines located in the Eastern Cordillera Basin, Colombia. The waters analyzed in this paper are from exploited coal beds, located up to 0.73 km deep, which emerge along with the local fault systems.The hydrochemical facies were classified based on the concentration of major ions by inferring the equilibrium state and rock water source. The main hydrochemical facies presented in the groundwater study are SO_4-Ca-Mg, HCO_3-Ca, HCO_3-Ca-Mg, and SO_4-HCO_3 mixed waters. We used geothermometric equations to estimate the most probable temperature under in-situ conditions and the propagation of errors theory to test the results. The geothermal gradient in the study area is close to 30℃/km, which is consistent with measurements from oil wells within the study area. Principal Component Analysis was used to explain factors affecting formation water composition and hydrogeochemical evolution of aquifers.

Fast magnitude determination using a single seismological station record implementing machine learning techniques

In this work a Support Vector Machine Regression（SVMR） algorithm is used to calculate local magnitude（MI） using only five seconds of signal after the P wave onset of one three component seismic station. This algorithm was trained with 863 records of historical earthquakes, where the input regression parameters were an exponential function of the waveform envelope estimated by least squares and the maximum value of the observed waveform for each component in a single station. Ten-fold cross validation was applied for a normalized polynomial kernel obtaining the mean absolute error for different exponents and complexity parameters. The local magnitude（MI） could be estimated with 0.19 units of mean absolute error. The proposed algorithm is easy to implement in hardware and may be used directly after the field seismological sensor to generate fast decisions at seismological control centers, increasing the possibility of having an effective reaction.

Earthquake distribution and lithospheric rheology beneath the Northwestern Andes, Colombia

The rheological behavior of the lithosphere beneath the Northwestern(NW)Andes(Colombian)remains uncertain under a complex geological setting.Here,we analyze the earthquake distribution and the stress drop on the western and the eastern of the transition area between the Upper Magdalena Valley(UMV)and the Middle Magdalena Valley(MMV),a zone related to a plate tectonic transition from steeper to flatter subduction style slabs(Nazca and Caribbean plates).Our results consistently explain the tectonic and geodynamic context of the study area supported in two rheological profiles,which reveal the brittle/ductile transition of the lithospheric crust and mantle and allow to constrain the lithospheric rheological thickness.The subduction phenomenon of the Nazca Plate under the South American Plate is observed in the western zone.In the eastern region,we find a remarkable aseismic zone under the Eastern Cordillera below 20-km-deep,which made more difficultan accurate estimation of the crust/mantle boundary.This seismic particularity leads us to support the hypothesis of a delamination process due to the tectonic overload generated by the Eastern Cordillera,and that promotes thermal anomalies.Our results also suggest that the earthquake dataset correlated with rheological estimations may offer a consistent interpretation of the mechanical behavior of the lithosphere.