Seismic Velocity Structure of the Shallow Part of the Alpine Fault and Gravity Study of the Basement Features in the Whataroa River Flood Plain, Central Westland, South Island

<p>The deep and middle sections of the Alpine fault have extensively been studied, however, the shallow part has had relatively minor geophysical attention. This study focuses on the basement geometry and the determination of the upper-crustal velocity structure of the Alpine fault in the vicinity of the Whataroa River flood plain in Central Westland, South Island. Data from a temporary gravity survey collected in November 2006, the GNS gravity database and four of the westernmost shot gathers from the SIGHT96's transect 1 were used for this project. A ray-tracing software was used to establish the velocity structure of the shallow part of the Alpine fault. Seismic velocities decrease to 3.8 km/s immediately southeast of the mylonite strip, which is adjacent to the Alpine fault's ramp heading towards the fault's surface trace from the southeast or from depth. Velocities of 5 km/s reach 2 km depth to the southeast of the Alpine fault's ramp. Results of the gravity and seismic models coincide in the positions and the dimensions of two northwest-orientated glacial overdeepings. The strike of their alignment is offset to the northeast by 3.5 km and is sub-parallel to the mouth of the Whataroa River. We propose that these kettle holes, thought to have been carved successively during the Waimea and Otira glaciations, are the beheaded river mouth of the Whataroa river. By supposing that the furthest kettle hole was carved during the Waimea glaciation, the 3.5 km offset thus corresponds to 140 Ka of dextral slip on the Alpine fault, we could approximate the mean displacement rate over the time interval of 140-18 Ka of 25 mm/yr.</p>

Seismic Velocity Structure of the Shallow Part of the Alpine Fault and Gravity Study of the Basement Features in the Whataroa River Flood Plain, Central Westland, South Island

<p>The deep and middle sections of the Alpine fault have extensively been studied, however, the shallow part has had relatively minor geophysical attention. This study focuses on the basement geometry and the determination of the upper-crustal velocity structure of the Alpine fault in the vicinity of the Whataroa River flood plain in Central Westland, South Island. Data from a temporary gravity survey collected in November 2006, the GNS gravity database and four of the westernmost shot gathers from the SIGHT96's transect 1 were used for this project. A ray-tracing software was used to establish the velocity structure of the shallow part of the Alpine fault. Seismic velocities decrease to 3.8 km/s immediately southeast of the mylonite strip, which is adjacent to the Alpine fault's ramp heading towards the fault's surface trace from the southeast or from depth. Velocities of 5 km/s reach 2 km depth to the southeast of the Alpine fault's ramp. Results of the gravity and seismic models coincide in the positions and the dimensions of two northwest-orientated glacial overdeepings. The strike of their alignment is offset to the northeast by 3.5 km and is sub-parallel to the mouth of the Whataroa River. We propose that these kettle holes, thought to have been carved successively during the Waimea and Otira glaciations, are the beheaded river mouth of the Whataroa river. By supposing that the furthest kettle hole was carved during the Waimea glaciation, the 3.5 km offset thus corresponds to 140 Ka of dextral slip on the Alpine fault, we could approximate the mean displacement rate over the time interval of 140-18 Ka of 25 mm/yr.</p>

India–European Union Trade Integration: An Analysis of Current and Future Trajectories

In a dynamic global environment of increased economic interdependence, nations are more than ever seeking to remove barriers to trade, despite growing trends of protectionism. In this context, India and the EU-27 have initiated talks for the establishment of a Bilateral Trade and Investment Agreement (BTIA) in an attempt to bring their economies together. However, after 16 rounds of negotiations, the failure to conclude this agreement has raised questions regarding the benefits of the agreement to India. This study attempts to examine the current trade scenario and the effects of the proposed regional trade agreement by estimating a structural gravity model. This study employs the Poisson Pseudo Maximum Likelihood (PPML) estimator for analysing the trade-creation and trade-diversion effects of the BTIA to overcome the shortcomings of ordinary least square (OLS) estimators. For the empirical analysis, the merchandise export data from the Gravity database has been taken for a period of 19 years from 2001 to 2019. The results indicate that the BTIA could lead to trade creation and trade diversion, highlighting the need for a re-evaluation of India’s trade policy. JEL Classification: F10, F13, F14, F15, O24

The first pan-Alpine surface-gravity database, a modern compilation that crosses frontiers

The AlpArray Gravity Research Group (AAGRG), as part of the European AlpArray program, focuses on the compilation of a homogeneous surface-based gravity data set across the Alpine area. In 2017 10 European countries in the Alpine realm agreed to contribute with gravity data for a new compilation of the Alpine gravity field in an area spanning from 2 to 23∘ E and from 41 to 51∘ N. This compilation relies on existing national gravity databases and, for the Ligurian and the Adriatic seas, on shipborne data of the Service Hydrographique et Océanographique de la Marine and of the Bureau Gravimétrique International. Furthermore, for the Ivrea zone in the Western Alps, recently acquired data were added to the database. This first pan-Alpine gravity data map is homogeneous regarding input data sets, applied methods and all corrections, as well as reference frames. Here, the AAGRG presents the data set of the recalculated gravity fields on a 4 km × 4 km grid for public release and a 2 km × 2 km grid for special request. The final products also include calculated values for mass and bathymetry corrections of the measured gravity at each grid point, as well as height. This allows users to use later customized densities for their own calculations of mass corrections. Correction densities used are 2670 kg m−3 for landmasses, 1030 kg m−3 for water masses above the ellipsoid and −1640 kg m−3 for those below the ellipsoid and 1000 kg m−3 for lake water masses. The correction radius was set to the Hayford zone O2 (167 km). The new Bouguer anomaly is station completed (CBA) and compiled according to the most modern criteria and reference frames (both positioning and gravity), including atmospheric corrections. Special emphasis was put on the gravity effect of the numerous lakes in the study area, which can have an effect of up to 5 mGal for gravity stations located at shorelines with steep slopes, e.g., for the rather deep reservoirs in the Alps. The results of an error statistic based on cross validations and/or “interpolation residuals” are provided for the entire database. As an example, the interpolation residuals of the Austrian data set range between about −8 and +8 mGal and the cross-validation residuals between −14 and +10 mGal; standard deviations are well below 1 mGal. The accuracy of the newly compiled gravity database is close to ±5 mGal for most areas. A first interpretation of the new map shows that the resolution of the gravity anomalies is suited for applications ranging from intra-crustal- to crustal-scale modeling to interdisciplinary studies on the regional and continental scales, as well as applications as joint inversion with other data sets. The data are published with the DOI https://doi.org/10.5880/fidgeo.2020.045 (Zahorec et al., 2021) via GFZ Data Services.

Gravity data collection with a CG5 gravitymeter for densification of the gravity data around the AUT1 IHRF station

&lt;p&gt;Within the GeoGravGOCE project, funded by the Hellenic Foundation for Research Innovation, a main goal has been the densification of the available land gravity database around the eastern part of the city of Thessaloniki, Greece, where the core International Height Reference Frame (IHRF) station AUT1 is located in order to improve regional geoid and potential determination. Hence it was deemed necessary to densify the available gravity data within radiuses of 10 km, 20 km, 50 km and 100 km from the AUT1 core IHRF site. In that frame, and given the geological complexity of the region surrounding Thessaloniki and the significant variations of the terrain, gravity campaigns were appropriately designed and gravity measurements were carried out in order to densify the database and cover as much as possible traverses of varying altitude. The measurements have been carried out with the CG5 gravity meter of the GravLab group and dual-frequency GNSS receivers in RTK mode for orthometric height determination. In this &amp;#160;study we provide details of the gravity campaigns, the measurement principle and the finally derived gravity and free-air gravity anomalies. The mean measurement accuracy achieved was at the ~20 &amp;#956;Gal level for the gravity measurements and ~3 cm for the orthometric heights. In all cases the final derived gravity value was based on the absolute point established by the GravLab team at the AUTH seismological station premises with the A10 (#027) absolute gravity meter.&lt;/p&gt;

The first pan-Alpine surface-gravity database, a modern compilation that crosses frontiers

The AlpArray Gravity Research Group (AAGRG), as part of the European AlpArray program, focuses on the compilation of a homogeneous surface-based gravity dataset across the Alpine area. From this data set, Bouguer- and Free Air anomalies are calculated and presented here. In 2016/17 ten European countries in the Alpine realm have agreed to contribute with gravity data for a new compilation of the Alpine gravity field in an area from 2° to 23° East and from 41° to 51° North. This compilation relies on existing national gravity databases and, for the Ligurian and the Adriatic seas, on ship-borne data of the Bureau Gravimétrique International. Furthermore, for the Ivrea zone in the Western Alps, recently acquired data were added to the database. This first pan-Alpine gravity data map is homogeneous regarding input data sets, applied methods and all corrections as well as reference frames. Here, the AAGRG presents the data set of the recalculated gravity fields on a 4 km × 4 km grid for public release, 2 km × 2 km for special request. The final products also include calculated values for mass/bathymetry corrections of the measured gravity at each grid point, as well as height. This allows users to use later customized densities for their own calculations of mass corrections. Correction densities used are 2670 kg m−3 for landmasses, 1030 kg m−3 for water masses above and −1640 kg m−3 below the ellipsoid. The correction radius was set to the Hayford zone O2 (167 km). The new Bouguer anomaly is station completed (CBA) and compiled according to the most modern criteria and reference frames (both positioning and gravity), including atmospheric corrections. Special emphasis was put on the gravity effect of the numerous lakes in the study area, which can have an effect of up to 5 mGal for gravity stations located at shorelines with steep slopes, e.g., for the rather deep reservoirs in the Alps. The results of an error statistic based on cross validations and/or interpolations residuals is provided for the entire database. As an example, the interpolation residuals of the Austrian data set range between about −8 and +8 mGal, the cross-validation residuals between −14 mGal and +10 mGal; standard deviations are well below 1 mGal. The accuracy of the newly compiled gravity database is close to ±5 mGal for most areas. A first interpretation of the new map shows that the resolution of the gravity anomalies is suited for applications ranging from intra-crustal to crustal scale modelling to interdisciplinary studies on the regional and continental scales as well as applications as joint inversion with other datasets. The data will be published with the DOI https://doi.org/10.5880/fidgeo.2020.045 (Zahorec et al., 2020) when the final paper is accepted. In the meantime, the data is accessible via this temporary review link: https://dataservices.gfz-potsdam.de/panmetaworks/review/fdc35a9f6551b01b6152ee1af7b91a5a0c3de5341d067644522c192ad7f25e7f.

Shallow structure of Los Humeros (LH) caldera and geothermal reservoir from magnetotellurics and potential field data

SUMMARY This study focuses in the analysis of the internal structure of the upper 3 km of Los Humeros (LH) caldera and the relation of electrical and hydrothermal anomalies. For this purpose, we measured, processed and interpreted 78 broad-band magnetotelluric (MT) soundings. We performed a 3-D inversion of the data set (ModEM) using all MT soundings, although only half of the available frequencies per sounding due to limited computed power. We also carried out the 2-D inversions (NLCG) of the invariant determinant along two orthogonal profiles (EW and NS) crossing the caldera structure; their comparison yields similar resistivity and structural models results. The resistivity modelling is complemented with the results of a joint 3-D inversion of an accurate gravity database of 720 stations, and total field aeromagnetic data (SGM) from the caldera crater. The combined results provide novel details about the structure of the shallow geothermal reservoir of the resurgence caldera complex hosting the active hydrothermal system. Density and resistivity models show the existence of a composed crater basin structure separated by an EW high-density structure; the northern basin is associated to the LH crater, whereas the southern basin associates to the emergent Los Potreros (LP) caldera basin. The magnetization model indicates that there is a common source for the magnetic volcanic products observed at the caldera surface, and that the LP fault is the more magnetized fault of the geothermal system. The propylic zoning under the geothermal field, which according to the MT model results has resistivities above ∼100 Ω-m, was extrapolated using this and additional criteria to obtain the distribution of other hypothetical propylitic zones of hydrothermal potential.