High Vp Research Articles

High‐Pressure Melting Experiments of Fe3C and a Thermodynamic Model of Fe‐C Liquids for the Earth's Core

AbstractMelting experiments of Fe3C were conducted to 85 GPa in laser‐heated diamond anvil cells with in situ X‐ray diffraction and post‐experiment textural observation. From the determined pressure‐temperature conditions of the melting curve for Fe3C, together with literature data on the melting point of diamond and eutectic point of the system Fe‐Fe3C/Fe7C3 under high pressures, we established a self‐consistent thermodynamic model for high‐pressure melting of the system Fe‐C including the mixing parameters for liquids. The results show that mixing of Fe and C liquids is negatively nonideal from 1 bar to the pressure at the center of the Earth. The departure from ideal mixing becomes progressively larger with increasing pressure, which leads to greatly stabilized liquids under core pressures. The modeled carbon content in eutectic melts under core pressures is 3.3–4.4 wt%. From the Gibbs free energy, we derived an internally consistent parameters for Fe‐C outer cores which included the crystallizing points at their bottoms, isentropic thermal profiles, and densities and longitudinal seismic wave speeds (Vp). While the addition of carbon in excess of the eutectic melt composition effectively reduces the density of iron liquid, the Vp of iron liquid is not greatly changed. Therefore, the low density and high Vp of PREM relative to pure iron cannot be reconciled by an Fe‐C liquid. Therefore, the Earth's core cannot be approximated by the system Fe‐C and should include another light element.

Localization of Deformation on Faults Driven by Fluids During the L’Aquila 2009 Earthquake

AbstractCoseismic rupture and aftershock development on a fault plane are complex and heterogeneous processes. The Mw 6.1 L’Aquila 2009 normal faulting earthquake is a perfect case to explore how fault geometry and rheology influence the rupture process and aftershocks distribution. In this study, we use for the first time a dense set of earthquake data to obtain enhanced images of the causative normal fault structure to the kilometer scale. The hypocenter of the emergent onset of the mainshock took place within a low Vp/Vs volume, while the large coseismic slip occurred a few kilometers above, as the rupture propagated through a high Vp and high Vp/Vs fluid‐filled rock volume. The increase of Vp/Vs in the fault hanging wall during the sequence suggests a strong dehydration in the earthquake asperity, with an upward fluid pressure migration along the fault toward the host rock volume. We propose that the localization of deformation on the fault plane is favored by high fluid pressure, while the spreading of aftershocks on a wide volume around the fault is driven by the depletion of fluids from the slipped portion of the fault plane and migration to small segments within the fault host rocks.

Crustal and uppermost mantle structures of the North American Midcontinent Rift revealed by joint full-waveform inversion of ambient-noise data and teleseismic P waves

The Midcontinent Rift (MCR), hosting several world-class ore deposits, is the fossil remnant of a massive Mesoproterozoic rifting event (1.1 Ga) that did not lead to the formation of an ocean basin. To better understand the lithospheric processes associated with the rifting stage and its subsequent failure, we developed a novel full-waveform joint inversion method using ambient noise data and teleseismic P waves for this seismically inactive region. We apply this approach to three years (2011-2013) of seismic recordings from the Superior Province Rifting EarthScope Experiment (SPREE) (~12 km average station spacing) and the USArray Transportable Array (~70 km average station spacing), and obtain a new 3D high-resolution Vs model down to 100 km depth, as well as Vp and density models down to 60 km depth. The model shows major velocity anomalies in agreement with previous seismic studies for the western arm of the MCR. In particular, we observe high density (2.8-3.0 g/cm3), Vp (6.3-6.5 km/s), and Vs (3.6-3.7 km/s) structures in the shallow upper crust within the rift, likely associated with volcanic rocks. Similar to a previously identified underplated layer, we also observe extensive normal-to-high Vs (3.8-4.2 km/s) along the whole rift axis and Vp (6.8-7.5 km/s) beneath the northern segment of the rift within the lower crust. However, the Vs and Vp values are lower than average for typical underplated materials. We suggest that this underplated layer may represent a combination of different intrusive rock types (e.g., gabbro, anorthosite) developed during magma differentiation processes, or contamination of the mafic magma by surrounding crustal material, or intrusions of sills.

Subsurface anatomy of the Irazú–Turrialba volcanic complex, inferred from the integration of local and ambient seismic tomographic methods

SUMMARY Irazú and Turrialba are a twin volcanic complex that marks a distinct stop in volcanism along the Central America volcanic arc. We present a new traveltime velocity model of the crust beneath Irazú and Turrialba volcanoes, Costa Rica, and interpret it considering the results of previous ambient noise tomographic inversions. Data were acquired by a temporary seismic network during a period of low activity of the Irazú–Turrialba volcanic complex in 2018–2019. Beneath the Irazú volcano, we observe low P-wave velocities (VP = 5 km s−1) and low velocity ratios (VP/VS = 1.6). In contrast, below the Turrialba volcano, we observe low S-wave velocities (VS = 3 km s−1) and a high VP/VS (= 1.85) anomaly. We found that locations of low VP and VS anomalies (−15 %) correspond well with shear wave velocity anomalies retrieved from ambient noise tomography. At shallower depths, we observe high VP and VS anomalies (+15 %) located between the summits of the volcanoes. Subvertical velocity anomalies are also observed at greater depths, with high VP and VS anomalies appearing at the lower limits of our models. We propose a complex structure of an intermediate magmatic reservoir, presenting multiphase fluid states of a liquid-to-gas transition beneath Irazú and a juvenile store of magmatic fluid beneath Turrialba, while shallow fluid transport provides evidence of magmatic–hydrothermal interactions.

Structure of shallow magma sources beneath Augustine Volcano (Alaska) inferred from local earthquake tomography

Augustine is an active stratovolcano occupying almost entirely a small island in the Cook Inlet in Alaska. In this study, we use the arrival time data from local seismicity recorded by 15 permanent seismic stations deployed on the flanks of Augustine Volcano by the Alaska Volcano Observatory and invert them by the body wave local earthquake tomography. The resulting model includes the 3D distributions of the P and S wave velocities (Vp and Vs), Vp/Vs ratio and the relocated seismic events. The resolved area extends down to the depth of 2 km below sea level (b.s.l). At shallow depths, within the edifice, we observe a contrasted anomaly with very high Vp, low Vs and very high Vp/Vs, which represents the rigid volcano core composed of igneous rocks (high Vp), but strongly fractured and saturated with fluids and melts (low Vs). At larger depths, below sea level, we retrieve a columnar anomaly of high Vp/Vs ratio representing the magma conduit. On the top of this anomaly, there is a zone with low Vp/Vs coinciding with the strong seismicity cluster, which is associated with the degassing of deep fluids.

High-resolution 3D crustal velocity structure imaging in the middle eastern boundary of the Sichuan-Yunnan Rhombic block

In this study, high-resolution VP and VP/VS models of the middle eastern boundary of the Sichuan-Yunnan Rhombic block were obtained based on a long-term dense observation array, with a horizontal resolution of 5 km and a depth resolution of 2 km. The models reveal that different fault zones have complex medium structures. The obviously low VP and high VP/VS anomalies in the shallow layers of the south section of Zemuhe fault zone and the north section of the Xiaojiang fault zone reflect the Quaternary sedimentary characteristics of rifted basins such as the Ningnan and Qiaojia basins. Low VP and heterogeneous VP/VS anomalies along the Sikai-Jiaojihe fault zone may reflect differences in rock composition. The interior of the Xiaojiang fault zone and its eastern side are characterized by complex segmentation. The high VP and high VP/VS along the northern Xiaojiang fault zone and the Zhaotong-Ludian fault zone basically coincide with the distribution of the Emeishan basalt, which indicates that the two fault zones are the main channels for the Emeishan basalt to intrude into the upper crust after the eruption. In addition, our models also revealed the seismogenic environment of moderate and strong earthquakes. The Ludian Ms 6.5 earthquake and the Qiaojia Ms 5.0 earthquake occurred at the boundary zones between high and low VP or VP/VS anomalies, thus resulting in stress accumulation. The L-shaped low VP anomaly at depths of 8–12 km in the source area of the Ludian Ms 6.5 earthquake coincides with the distribution of aftershocks, which reveals that the low VP anomaly controls the distribution of aftershocks. The obvious boundary zones between high and low VP and VP/VS anomalies above the source area of the Ludian Ms 6.5 earthquake may be at risk for major earthquakes in the future.

Tectonic Structure of Northern Sumatra Region Based on Seismic Tomography of P and S Wave Velocity

The tectonic setting of Sumatra Island is strongly influenced by the oblique subduction of the Indo-Australian Plate, which subducts the Eurasian Plate at a speed of 52–60 mm/year. The movement of these plates resulted in the Northern Sumatra region having seismic sources from tectonic and volcanic activity. The data used in this study is in the form of seismic wave travel-time recorded by numerous seismic stations in the research area from January 2012 to December 2020. The data comes from 5,003 earthquakes recorded by the BMKG seismic network. The inversion is a simultaneous inversion between seismic velocity models (Vp and Vs) and hypocenter parameters by applying a double-difference seismic tomography algorithm. Tomogram results in parts of Aceh (Singkil and Subulussalam) and North Sumatra (Pakpak Bharat and Dairi) at a depth of 0 km show negative perturbations in Vp and Vs values and high Vp/Vs values. The anomaly is most likely related to cracks in fluid-saturated rocks. The tomograms in the south of Lake Toba at depths of 30 km and 40 km have high Vp and Vs perturbation values and low Vp/Vs values. This anomaly indicates a magma supply line that is no longer active or has cooled for a long time. Based on the seismic tomography modeling results, the subducted Indo-Australian Plate to the Eurasian Plate is visible in the study area.

Seismic Tomography of Nabro Caldera, Eritrea: Insights Into the Magmatic and Hydrothermal Systems of a Recently Erupted Volcano

AbstractUnderstanding the crustal structure and the storage and movement of fluids beneath a volcano is necessary for characterizing volcanic hazard, geothermal prospects and potential mineral resources. This study uses local earthquake traveltime tomography to image the seismic velocity structure beneath Nabro, an off‐rift volcano located within the central part of the Danakil microplate near the Ethiopia‐Eritrea border. Nabro underwent its first historically documented eruption in June 2011, thereby providing an opportunity to analyze its post‐eruptive state by mapping subsurface fluid distributions. We use a catalog of earthquakes detected on a temporary seismic array using machine learning methods to simultaneously relocate the seismicity and invert for the three‐dimensional P‐ and S‐wave velocity structures (VP, VS) and the ratio between them (VP/VS). Overall, our model shows higher than average P‐ and S‐wave velocities, suggesting the presence of high‐strength, solidified intrusive magmatic rocks in the crust. We identify an aseismic region of low VP, low VS, and high VP/VS ratio at depths of 6–10 km b.s.l., interpreted as the primary melt storage region that fed the 2011 eruption. Above this is a zone of high VS, low VP, and low VP/VS ratio, representing an intrusive complex of fractured rocks partially saturated with over‐pressurized gases. Our observations identify the persistence of magma in the subsurface following the eruption, and track the degassing of this melt through the crust to the surface. The presence of volatiles and high temperatures within the shallow crust indicate that Nabro is a viable candidate for geothermal exploration.

Indian plate blocked by the thickened Eurasian crust in the middle of the continental collision zone of southern Tibet

The relationship of the crustal contact between the Indian and Eurasian plates is a key issue in understanding crustal thickening and the subduction of the Indian lithosphere beneath the Qinghai-Tibetan Plateau. Across the middle of the Yarlung-Zangbo Suture (YZS), we deployed an ∼450-km-long SN-trending wide-angle reflection/refraction profile to observe the P-wave velocity (vP) structure beneath the northern Himalaya and the southern plateau. Our results show that, 1. the high vP (∼7.1 ​km/s) indicates that the Indian lower crust extends no more than 50 ​km north of the YZS. 2. The lower crust beneath the southern part of the plateau features an extremely low vP (<6.7 ​± ​0.2 ​km/s). 3. Compared with the velocities of several typical crustal lithologies in different temperature regimes, the low vP in the lower crust can be explained by felsic-intermediate granulite, which has prevented the lower crust from further eclogitization. We propose that the dip angle of the Indian lithospheric slab beneath the YZS is partly controlled by the composition of the lower crust of the plateau. In the northern middle YZS, the crust of the southern plateau is too thick and blocks the northward advancement of the Indian lower crust, resulting in the subduction of the Indian lithospheric slab into the upper mantle. The lower crust in western and eastern Lhasa is dominated by a mafic composition, and it was delaminated after eclogitization before the Miocene. The void zone generated by delamination favors the flattening and underthrusting of the Indian lower crust.

3-D imaging of the Balmuccia peridotite body (Ivrea–Verbano zone, NW-Italy) using controlled source seismic data

SUMMARY We provide new results from a controlled-source seismic experiment on the deepest part of the Val Sesia crust–mantle section of the Ivrea–Verbano zone (IVZ) in the Italian Alps. The IVZ is a tilted, almost complete section through the continental crust and exposes gabbros and peridotites in the structurally deepest level, coinciding with high-resolution gravity anomalies imaging the Ivrea geophysical body. The seismic experiment SEIZE (SEismic imaging of the Ivrea ZonE) was conducted along two crossing profiles: an NNE-SSW profile of ∼11 km length and an E-W profile of ∼16 km length. 432 vibration points were recorded with 110 receivers resulting in 24 392 traveltime picks. Inversion methods using Markov chain Monte Carlo techniques have been used to derive an isotropic 3-D P-wave velocity model based on first break traveltimes (refracted phases) from controlled source seismic data. Resulting seismic P-wave velocities (Vp ) range from 4.5 to 7.5 km s−1, with an expected general trend of increasing velocities with depth. A sharp velocity change from low Vp in the West to high Vp in the East marks the Insubric Zone (ISZ), the Europe–Adria plate boundary. The most prominent feature of the 3-D tomography model is a high-velocity body (Vp increases from 6 to 7.5 km s−1) that broadens downwards. Its pointy shape peaks the surface East of Balmuccia at a location coincident with the exposed Balmuccia peridotite. Considering rock physics, high-resolution gravity and other geophysical data, we interpret this high-velocity body as dominantly composed of peridotite. The dimension of this seismically imaged peridotite material is far bigger than interpreted from geological cross-sections and requires a revision of previous models. The interpretation of ultramafic bodies in the IVZ as fragments of mantle peridotites interfingered in the crust during pre-Permian accretion is not supported by the new data. Instead, we revive a model that the contact between the Balmuccia peridotite and the Permian mafic magmas might represent a fossil continental crust–mantle transition zone.

Modeling and inversion in acoustic-elastic coupled media using energy-stable summation-by-parts operators

Seismic data acquired at the seafloor are valuable in characterizing the subsurface and monitoring producing hydrocarbon fields. To fully use such data, a stable, accurate, and efficient numerical scheme is needed that accounts for acoustic and elastic wave propagation, their interaction at the seafloor interface, and for sources and receivers placed on either side of that interface. Existing methods either make incorrect assumptions or have high implementation and computational costs. We have developed a high-order finite-difference summation-by-parts framework for the acoustic-elastic wave equations in second-order form (in terms of displacements in the solid and an extension of velocity potential in the fluid). Our modified discretization of the elastic operator overcomes the dispersion errors known to plague displacement-based schemes in the high VP/ VS limit. We weakly impose boundary and interface conditions using simultaneous approximation terms, leading to an energy-stable numerical scheme that rigorously handles point injection and extraction. The fully discrete system is self-adjoint after a time reversal and a sign flip and is furthermore a high-order accurate discretization of the continuous problem. The self-adjointness ensures that forward and adjoint wavefields are computed with similar accuracy and simplifies gradient computation for inversion purposes. We find that our numerical scheme achieves accuracy comparable to a more computationally expensive spectral-element method and demonstrate its application to full-waveform inversion using the Marmousi2 model.

Local Earthquake Seismic Tomography Reveals the Link Between Crustal Structure and Volcanism in Tenerife (Canary Islands)

AbstractVolcanic activity on Tenerife Island is extremely diverse. Three radial rift zones are characterized by cinder cones from basaltic fissure eruptions. A triple junction in central Tenerife exhibits a complex of merged, predominantly phonolitic, stratovolcanoes. The Las Cañadas caldera and widespread ignimbrite deposits reveal high explosive potential. We investigated the crustal and upper mantle structure beneath Tenerife using local earthquake data recorded by two dense seismic networks on the island. For our tomographic inversion, we selected &gt;130,000 P‐ and S‐wave arrivals from ∼6,300 events that occurred during seismic unrests in 2004–2005 and 2017–2021. Synthetic tests confirmed that we could robustly resolve seismic velocity structures to ∼20 km depth. In the upper crust (down to ∼7 km) beneath central Tenerife, a prominent high‐velocity anomaly represents the rigid core of the volcanic complex; at greater depths, a strong low‐velocity anomaly reveals abrupt crustal thickening. Vp and Vs contour lines of 5.2 and 2.85 km/s, respectively, reveal Moho depth variation; crustal thickness beneath Las Cañadas reaches ∼17 km, whereas that beneath other parts of Tenerife is ∼10 km. An anomaly at ∼5 km beneath the caldera with low Vp, low Vs, and high Vp/Vs might be associated with a major phonolitic magma reservoir. Similar anomalies at ∼ sea level may represent shallow magma sources responsible for recent eruptions. Seismicity occurs in a columnar area of high Vp, high Vs, and low Vp/Vs, and may represent hydrothermal fluid migration through brittle media. Based on our results, we constructed a conceptual model of volcanic activity on Tenerife.

SEISMIC IMAGING BENEATH SUMATRA ISLAND AND ITS SURROUNDINGS, INDONESIA, FROM LOCAL-REGIONAL P-WAVE EARTHQUAKE TOMOGRAPHY

Sumatra Island and its surroundings, Indonesia, are one of the most active tectonics in the world. The Aceh-Andaman earthquake, one of the most destructive earthquakes in the world, occurred there. It has attracted many earth scientists to apply various methods, including seismic tomography, to understand the island’s subsurface structure and tectonic system. This study is the first to delineate subsurface imaging beneath the island and its surroundings using a local-regional earthquake catalogue from the Indonesian Agency for Meteorology, Climatology, and Geophysics (BMKG) seismicnetwork. The tomographic imaging of P-wave (Vp) conducted in this study has successfully delineated subduction slabs (high Vp), partial melting zones (low Vp), volcanic arcs (low Vp), and Sumatran Fault zones (low Vp). The relationship between the subduction zone and the volcanic arc on the island can be seen on several vertical sections where a partial melting zone occurs at a depth of about 100 km, which functions as magma feeding for some volcanoes on the island. The oceanic slab model also exhibits a more pronounced and steeper slope towards the southern regions of Sumatra Island, possibly attributed to the slab’s aging process in that direction. The results highlight the importance of the BMKG seismic network in imaging local-regional subsurface structures beneath Indonesia’s archipelago, especially for the main islands such as Sumatra.

Seismic Structure Beneath the Molucca Sea Collision Zone from Travel Time Tomography Based on Local and Regional BMKG Networks

The Molucca Sea Plate, and Sangihe and Halmahera plates have a complex tectonic setting and interact to create the Molucca Sea Collision Zone. We re-picked 1647 events recorded from 2010 to 2017 from 32 of The Agency for Meteorology, Climatology, and Geophysics (BMKG) stations and obtained P- and S-arrivals of ~17,628 phases. Hypocenter locations were determined using the software NonLinLoc. Then, we performed a travel time tomography in order to image the subsurface and approximate the Molucca Sea Plate subduction angle beneath Sulawesi’s north arm, the relationship subduction zone and volcanic activity in Halmahera, and depth comparison of the Molucca Sea Plate. Our results show that (i) high Vp, high Vs, and low Vp/Vs are associated with the Molucca Sea Plate beneath Sulawesi’s north arm, and the approximate subduction angle is ~40°. (ii) Low Vp, low Vs, and high Vp/Vs beneath the northern and southern Halmahera Volcanic Arc are associated with a possible magma source. Volcanoes in the north have experienced eruptions and are dormant in the south. This group of volcanoes is connected by partial melting above the Molucca Sea Plate subducts to the east. (iii) High Vp, high Vs, and low Vp/Vs are interpreted as double subduction of the Molucca Sea Plate. It is submerged deeper in the north compared with the south, which is nearer to the surface.

Structure of the Crustal Magmatic System in the Geysers-Clear Lake Area (Northern California) Imaged by Adjoint-State Travel-Time Tomography

Abstract The Clear Lake volcanic field (CLVF) in northern California powers the world’s largest geothermal power plant, the Geysers Geothermal Complex. Volcanic-type earthquakes, hot springs, and seepage of volcanic gas suggest possible volcanic eruptions in the future. In this study, we apply a recently developed adjoint-state travel-time tomography method to high-quality manually picked P- and S-wave travel-time data to create 3D crustal VP and VS models for the Geysers-Clear Lake area. The adjoint-state travel-time tomography method has advantages of computational efficiency, ease of parallel implementation, and high accuracy in dealing with complex media. Strong velocity heterogeneities are revealed in the Geysers-Clear Lake area and its surrounding regions. Within the overall high VP, high VS Coast Ranges, a low VP, low VS anomaly is imaged beneath Mount Hannah, which indicates the existence of a large magma chamber. Our tomographic results suggest a simplified three-layer magmatic model beneath the CLVF: the upper layer (&amp;lt;7 km) consists of some intrusions of silicic magma from beneath Mount Hannah to the Geysers Geothermal Field in the southwest and to the Wilbur Springs area east of Clear Lake; the median layer includes the main body of the magma chamber at 5–13 km in depth and in the shape of an oblate ellipsoid; and the lower layer includes some mafic intrusions and molten or partially molten volcanic rocks from the upwelling mantle. The detailed velocity heterogeneities revealed by the newly picked travel-time data with the adjoint-state travel-time tomography method provide necessary constraints on seismogenic, volcanic, and geothermal processes in the Geysers-Clear Lake area, which are also useful for the mitigation of geologic hazards in northern California.

Crustal Compositional Variations From Continental to Oceanic Domain: A VP/VS Ratio Study Across the Zhongsha Block, South China Sea

AbstractThe VP/VS ratio is an important property for understanding magmatic and tectonic processes at passive continental margins as it is an indicator of the crustal composition. To classify the dominant lithologies in the Zhongsha Block, South China Sea (SCS), we present a detailed VP/VS crustal model based on the independent tomographic inversion of P wave and S wave data. The average VP/VS in the crust of the Zhongsha Block is ∼1.77, indicating an overall felsic to intermediate composition lacking remnant magmatic intrusive rocks. The VP‐density relationship from gravity modeling suggests that the lower crust of the extended continental domain contains more greenschist and hence may have experienced metamorphism resulting from an elevated geotherm in the Northwest Sub‐basin either during the syn‐spreading or postspreading stage. The variability of the VP/VS ratio in the continental block is larger than that in the oceanic basin, showing distinct crustal properties. Several low VP/VS ratio anomalies (VP/VS &lt; 1.7) were found near tectonic boundaries and are interpreted to either result from felsic metamorphism during an interval of rifting, or during the migration of magma along faults and cracks in the postrift period. VP/VS ratios occurring in concert with high VP anomalies in the continent‐ocean transition zone support a mafic composition of metapelitic granulite, which was either formed by magmatic intrusions or contact with mantle melting that stem from the upwelling of the asthenospheric mantle during the initial break‐up and onset of the seafloor spreading stage in the SCS.

Depth-dependent crustal azimuthal anisotropy in the Salton Trough, southern California

We present new crustal models of azimuthally anisotropic P-wave velocity, isotropic P-wave velocity (Vp), isotropic S-wave velocity (Vs) and Vp/Vs ratio for the Salton Trough. High Vp/Vs ratio is revealed at depths of 2–8 km along the San Andreas Fault, implying the possible presence of fluids. High Vp and high Vp/Vs ratio (>1.8) structures of the mid-lower crust beneath the Salton Trough possibly reflect the underplated gabbroic rocks as a result of the extension-induced partial melting of the upwelling asthenospheric materials. The fast velocity directions (FVDs) generally correlate with the direction of the maximum horizontal compressive stress except that fault-parallel FVDs are found at main fault traces. However, the FVDs in the Salton Trough show complex features. The northern Slaton Trough basin (the northern Salton Sea basin and Coachella Valley basin) is dominated by NW-SE FVDs, which are possibly due to the active compression happening there. E-W oriented FVDs predominate the upper crust of the southern Salton Trough basin (the southern Salton Sea basin and Imperial Valley basin), possibly due to faulting and/or block rotation. As the depth increases (12–18 km), the FVDs to the south of the Salton Sea have an overall rotation and gradually become NW-SE. The depth-dependent variation of anisotropy orientation may be attributed to a large band of underlying heat source that probably causes a change of stress field by imposing thermal stress on overlying rocks. In all, our velocity models suggest that faults in the Salton Trough may bear a high risk of mechanical failures due to the complexities of stress distribution and geological structures as well as the presence of a large volume of fluids and heat.

Dual-chamber cardiac pacing short-term effect on left and right atria morphometric parameters and function

Abstract Funding Acknowledgements Type of funding sources: None. Background. Dual-chamber pacemaker implantation is a standard interventional treatment strategy for symptomatic sinus syndrome (SSS) or advanced atrioventricular block (AVB). It is already known that right ventricular pacing might have detrimental effects on cardiac function. However, knowledge about atrial pacing effect on left (LA) and right (RA) atria function is still lacking. Purpose. To assess the impact atrial pacing on left and right atria morphologic and functional parameters in patients after dual-chamber pacemaker implantation. Methods. We conducted a prospective study that included patients who received a dual-chamber pacemaker for an indication of AVB or SSS. A base rate of 40 bpm and no rate response in case of clear AVB indication or a base rate of 60 bpm and rate response if indication was SSS were chosen. A transthoracic echocardiography was done the next day after pacemaker implantation and after 1 and 3 months. To remove the impact of right ventricular pacing, patients with high VP percentage (&amp;gt;40%) were excluded from analysis. Patients were divided into two groups – group A with high AP (&amp;gt;50%), and group B – low AP (&amp;lt;50%). LA expansion fraction reflecting reservoir function, emptying - reflecting conduit, and active emptying reflecting "atrial kick" were analysed. To compare means the Mann Whitney U test, and for categorical variables – X² test were used. Results A total of n = 78 patients underwent dual-chamber implantation and signed informed consent. Due to significant structural heart disease or reduced ejection fraction (&amp;lt;50%) 7 patients were excluded from further analysis. Out of those, n = 21 were excluded due to a high VP percentage. Group A consisted of n = 26 and group B of – n = 24 patients. Average AP in group A was 63,5% and 68,3% at 1 and 3 months and 5,6% and 7,2% in group B respectively. The mean age (group A 74,5 SD 8,6 years vs group B 78,1 SD 8,0 years, p = 0,266), gender distribution (group A males 45,5% vs group B 48,4%, p = 0,774), and mean BMI (group A 26,4 SD 4,8 kg/m2 vs group B 29,5 SD 3,7 kg/m2, p = 0,202) did not differ significantly between the two groups. The mean left ventricular end diastolic diameter (LVEDD) and indexed LVEDD were not significantly different at baseline and did not change during the follow up period. The baseline LA and RA morphometric and functional parameters presented was not different at baseline between the two groups. The change in LA and RA functional parameters presented in figures. A tendency for a lower LA expansion fraction, active emptying fraction and LA ejection fraction were observed in group A. The trend was contant during 1 and 3 month follow-up periods. RA morphometric parameters did not change significantly between the two groups. Conclusion Impaired LA function in a higher percentage of atrial pacing is seen early after pacemaker implantation and could progress over time. Though, even longer observational period is needed. Abstract Figure. Abstract Figure.

The Rift and Continent‐Ocean Transition Structure Under the Tagus Abyssal Plain West of the Iberia

AbstractThe West Iberia margin is the focus of intense research since the 1980s, with some of the most exemplary geophysical cross‐sections and drilling expeditions. Those data sets have been used to create conceptual models of rifting used as a template to interpret margins worldwide. We present two collocated ∼350 km long lines of multi‐channel seismic (MCS) streamer data and wide‐angle seismic (WAS) data collected across the Tagus Abyssal Plain (TAP). We use travel‐times of first arrivals identified at WAS and reflected seismic phases identified at both WAS and MCS records to jointly invert for the P wave velocity (Vp) distribution and the geometry of a sediment unconformity, the top of the basement, and the Moho boundary. The Vp model shows that the TAP basement is more complex than previously inferred, presenting abrupt boundaries between five domains. Domain I under the foot of the slope and Domain III under the abyssal plain display Vp values and gradients of thin continental crust. In between, Domain II displays a steep Vp gradient and high Vp values at shallow depth that support that basement is made of exhumed partly serpentinized mantle. Domain IV and Domain V, further oceanward, have oceanic crust Vp structure. The new results support an unanticipated complex rift history during the initial separation of Iberia and America. We propose a geodynamic scenario characterized by two phases of extension separated by a jump of the locus of extension, caused by the northward propagation of the oceanic spreading center during the J‐anomaly formation, which terminated continental rifting.

Lithological Study of Mishrif, Rumaila, Ahmadi and Mauddud Formations Using Vp/ Vs Ratio, Acoustic Impedance and Well Logging at Amara Oil Field, Southern Iraq

The lithology of four formations from the Cretaceous period (Mishrif, Rumaila, Ahmadi, and Mauddud) was evaluated using the Acoustic Impedance and Vp/Vs ratio cross plot from Rock Physics Templates. Dipole sonic logs in Am-6-Am-10 well log were used to calculate compression velocity then the estimated shear velocity using Greenberg Castagna equations. RHOB and VP logs were used to calculate Acoustic Impedance. The ratio of Vp/Vs was measured then used with Acoustic Impedance colored by shale volume which is measured from gamma ray log, porosity and water saturation to estimate lithology type of the considered formations using cross plots and rock physics chart in the Techlog software. The lithology of the formations found to be of high porosity limestone alternating with hard limestone layers and the shale volume increases in the Ahmadi formation. The water bearing zone was found in all Formations, this zone is indicted by high Vp/ Vs ratio and low AI. The hydrocarbon bearing zones were indicated by low amount of both Acoustic Impedance and Vp/Vs ratio and this observation was shown in Mishrif and Mauddud formations.