Local Earthquake Tomography of Central Costa Rica: Transition from seamount to ridge subduction

The structure and seismicity of the subduction zone of centralCosta Rica have been investigated with local earthquake tomography down to ca. 50 km depth. Seismic traveltime data sets of three on- and offshore seismic networks were combined for a simultaneous inversion of hypocentre locations, 3-D structure of P-wave velocity and Vp/Vs ratio using about 2000 highquality events. The seismicity and slab geometry as well as Vp and Vp/Vs show significant lateral variation along the subduction zone corresponding to the changes of the incoming plate which consists of serpentinized oceanic lithosphere in the northwest, a seamount province in the centre and the subducting Cocos Ridge in the southeast of the investigation area. Three prominent features can be identified in the Vp and Vp/Vs tomograms: a high-velocity zone with a perturbation of 4–10 per cent representing the subducting slab, a low-velocity zone (10–20 per cent) in the forearc crust probably caused by deformation, fluid release and hydration and a low-velocity zone below the volcanic arc related to upwelling fluids and magma. Unlike previously suggested, the dip of the subducting slab does not decrease to the south. Instead, an average steepening of the plate interface from 30◦ to 45◦ is observed from north to south and a transition from a plane to a step-shaped plate interface. This is connected with a change in the deformation style of the overriding plate where roughly planar, partly conjugated, clusters of seismicity of regionally varying dip are observed. It can be shown that the central Costa Rica Deformation Belt represents a deep crustal transition zone extending from the surface down to 40 km depth. This transition zone indicates the lateral termination of the active part of the volcanic chain and seems to be related to the changing structure of the incoming plate as well

Astrometry and geodesy with radio interferometry: experiments, models, results

Summarizes current status of radio interferometry at radio frequencies between Earth-based receivers, for astrometric and geodetic applications. Emphasizes theoretical models of VLBI observables that are required to extract results at the present accuracy levels of 1 cm and 1 nanoradian. Highlights the achievements of VLBI during the past two decades in reference frames, Earth orientation, atmospheric effects on microwave propagation, and relativity.Comment: 83 pages, 19 Postscript figures. To be published in Rev. Mod. Phys., Vol. 70, Oct. 199

P and S velocity sturcture of the crust and the upper mantle beneath Central Java from local tomography inversion

Here we present the results of local source tomographic inversion beneath central Java. The data set was collected by a temporary seismic network. More than 100 stations were operated for almost half a year. About 13,000 P and S arrival times from 292 events were used to obtain three-dimensional (3-D) Vp, Vs, and Vp/Vs models of the crust and the mantle wedge beneath central Java. Source location and determination of the 3-D velocity models were performed simultaneously based on a new iterative tomographic algorithm, LOTOS-06. Final event locations clearly image the shape of the subduction zone beneath central Java. The dipping angle of the slab increases gradually from almost horizontal to about 70°. A double seismic zone is observed in the slab between 80 and 150 km depth. The most striking feature of the resulting P and S models is a pronounced low-velocity anomaly in the crust, just north of the volcanic arc (Merapi-Lawu anomaly (MLA)). An algorithm for estimation of the amplitude value, which is presented in the paper, shows that the difference between the fore arc and MLA velocities at a depth of 10 km reaches 30% and 36% in P and S models, respectively. The value of the Vp/Vs ratio inside the MLA is more than 1.9. This shows a probable high content of fluids and partial melts within the crust. In the upper mantle we observe an inclined low-velocity anomaly which links the cluster of seismicity at 100 km depth with MLA. This anomaly might reflect ascending paths of fluids released from the slab. The reliability of all these patterns was tested thoroughly

Joint Inversion of Active and Passive Seismic Data in Central Java

Seismic and volcanic activities in Central Java, Indonesia, the area of interest of this study, are directly or indirectly related to the subduction of the Indo-Australian plate. In the framework of the MERapi AMphibious EXperiments (MERAMEX), a network consisting of about 130 seismographic stations was installed onshore and offshore in Central Java and operated for more than 150 days. In addition, 3-D active seismic experiments were carried out offshore. In this paper, we present the results of processing combined active and passive seismic data, which contain traveltimes from 292 local earthquakes and additional airgun shots along three offshore profiles. The inversion was performed using the updated LOTOS-06 code that allows processing for active and passive source data. The joint inversion of the active and passive data set considerably improves the resolution of the upper crust, especially in the offshore area in comparison to only passive data. The inversion results are verified using a series of synthetic tests. The resulting images showan exceptionally strong low-velocity anomaly (−30 per cent) in the backarc crust northward of the active volcanoes. In the upper mantle beneath the volcanoes, we observe a low-velocity anomaly inclined towards the slab, which probably reflects the paths of fluids and partially melted materials in the mantle wedge. The crust in the forearc appears to be strongly heterogeneous. The onshore part consists of two high-velocity blocks separated by a narrow low-velocity anomaly, which can be interpreted as a weakened contact zone between two rigid crustal bodies. The recent Java Mw = 6.3 earthquake (2006/05/26-UTC) occurred at the lower edge of this zone. Its focal strike slip mechanism is consistent with the orientation of this contact

The 2018 European heatwave led to stem dehydration but not to consistent growth reductions in forests

Heatwaves exert disproportionately strong and sometimes irreversible impacts on forest ecosystems. These impacts remain poorly understood at the tree and species level and across large spatial scales. Here, we investigate the effects of the record-breaking 2018 European heatwave on tree growth and tree water status using a collection of high-temporal resolution dendrometer data from 21 species across 53 sites. Relative to the two preceding years, annual stem growth was not consistently reduced by the 2018 heatwave but stems experienced twice the temporary shrinkage due to depletion of water reserves. Conifer species were less capable of rehydrating overnight than broadleaves across gradients of soil and atmospheric drought, suggesting less resilience toward transient stress. In particular, Norway spruce and Scots pine experienced extensive stem dehydration. Our high-resolution dendrometer network was suitable to disentangle the effects of a severe heatwave on tree growth and desiccation at large-spatial scales in situ, and provided insights on which species may be more vulnerable to climate extremes

The 2018 European heatwave led to stem dehydration but not to consistent growth reductions in forests

Publisher Copyright: © 2022, The Author(s).Heatwaves exert disproportionately strong and sometimes irreversible impacts on forest ecosystems. These impacts remain poorly understood at the tree and species level and across large spatial scales. Here, we investigate the effects of the record-breaking 2018 European heatwave on tree growth and tree water status using a collection of high-temporal resolution dendrometer data from 21 species across 53 sites. Relative to the two preceding years, annual stem growth was not consistently reduced by the 2018 heatwave but stems experienced twice the temporary shrinkage due to depletion of water reserves. Conifer species were less capable of rehydrating overnight than broadleaves across gradients of soil and atmospheric drought, suggesting less resilience toward transient stress. In particular, Norway spruce and Scots pine experienced extensive stem dehydration. Our high-resolution dendrometer network was suitable to disentangle the effects of a severe heatwave on tree growth and desiccation at large-spatial scales in situ, and provided insights on which species may be more vulnerable to climate extremes.Peer reviewe

Influence of depth, temperature, and structure of a crustal heat source on the geothermal reservoirs of Tuscany: numerical modelling and sensitivity study

© 2016, Ebigbo et al.Granitoid intrusions are the primary heat source of many deep geothermal reservoirs in Tuscany. The depth and shape of these plutons, characterised in this study by a prominent seismic reflector (the K horizon), may vary significantly within the spatial scale of interest. In an exploration field, simulations reveal the mechanisms by which such a heat source influences temperature distribution. A simple analysis quantifies the sensitivity of potentially measurable indicators (i.e. vertical temperature profiles and surface heat flow) to variations in depth, temperature, and shape of the heat source within given ranges of uncertainty

From the Valdivia Fracture Zone to the Villarrica volcanic complex - seismic evidence of a link between subducted oceanic faults and volcanism

The south-central Chilean subduction zone was investigated at 39-40°S by a passive seismic experiment. The investigation area comprises the maximum slip of the great 1960 Mw 9.5 Valdivia earthquake. The incoming Nazca plate is permeated by a number of major fault zones including the Valdivia fault zone and the Mocha fault zone which seem to have behaved as a barriers for the rupture propagation of large earthquakes in the past. The investigated sector is also home to the Villarrica volcano - one of South America’s most active volcanoes. In the extension of the Valdiva fault zone we observed a cluster of increased seismicity in the subducting plate at depths between 80 km and 120 km, where dehydration of the subducting plate occurs. The focal plane solutions of this cluster show predominantly strike-slip motion. Tomographic images show decreased P- and Svelocity and increased ratio between the seismic cluster and the volcanic center of Villarrica, Quetrupillán and Lanin, corresponding to an increased content of fluids or melt. Additional geochemical investigations show that the magma of Villarrica volcano has an enhanced fluid signal compared to the other volcanoes of the Southern Volcanic Zone of Chile. It can be assumed that the Valdivia fault zone serves as the source for the fluids. Before the plate subducts, water can penetrate the plate through faults within the Valdivia fault zone. Serpentinization would build the water into minerals. Inside the subduction zone the Valdiva fault zone is reactivated by dehydration reactions at a depth of about 100 km. The released fluids rise towards the volcanic center causing the tomographic anomalies. At the end this leads to an increased degree of melting and a higher activity of Villarrica volcano