Seismicity relocation and fault structure near the Leech River Fault Zone, southern Vancouver Island

Relatively low rates of seismicity and fault loading have made it challenging to correlate microseismicity to mapped surface faults on the forearc of southern Vancouver Island. Here we use precise relocations of microsciesmicity integrated with existing geologic data, to present the first identification of subsurface seismogenic structures associated with the Leech River fault zone (LRFZ) on southern Vancouver Island. We used HypoDD double difference relocation method to relocate 1253 earthquakes reported by the Canadian National Seismograph Network (CNSN) catalog from 1985 to 2015. Our results reveal an ~8-10 km wide, NNE-dipping zone of seismicity representing a subsurface structure along the eastern 30 km of the terrestrial LRFZ and extending 20 km farther eastward offshore, where the fault bifurcates beneath the Juan de Fuca Strait. Using a clustering analysis we identify secondary structures within the NNE-dipping fault zone, many of which are sub-vertical and exhibit right-lateral strike-slip focal mechanisms. We suggest that the arrangement of these near-vertical dextral secondary structures within a more general NE-dipping fault zone, located well beneath (10-15 km) the Leech River fault (LRF) as imaged by LITHOPROBE, may be a consequence of the reactivation of this fault system as a right-lateral structure in the crust with pre-existing NNE-dipping foliations. Our results provide the first confirmation of active terrestrial crustal faults on Vancouver Island using a relocation method. We suggest that slowly slipping active crustal faults, especially in regions with pre-existing foliations, may result in microseismicity along fracture arrays rather than along single planar structures

An alternative Mesozoic geodynamic model for the evolution of the Central Coastal ranges of Peru: the Rio Cañete Basin

Integration of detailed stratigraphic, sedimentologic and tectonic studies of the Río Cañete Basin with opening and divergence rates of the South Atlantic Ocean, overriding plate velocity, trench migration, subducting age (Fig. 1) etc. and the protracted Mesozoic Farallon Plate oblique convergence parameters provide new lines of evidence to suggest an alternative model for the evolution of the Peruvian margin. These unorthodox model departures significantly from the classic and simplistic Andean Model used in the literature. The western margin of Gondwana experience severe lithosphere extension coeval with arc magmatism since at least Middle Triassic. Actually, only the uppermost Jurassic unit is displayed along the Río Cañete Basin, however, it is important to take into account that northward the Jurassic arc sequence terminates against the accreted Amotape/Olmos Terrain and it overlies the Late Triassic to Jurassic Pucara Group. Slab stagnation in the mantle transition zone near the upper and lower mantle boundary perhaps triggered shallow subduction, which in turn caused drowning and Jurassic arc volcanism termination. Slab flattening increased upper plate stress coupling transferring the stresses eastward and causing basement-core block uplift and changing provenance to quartz-rich. Slab breakoff occurred soon after the water-bearing serpentinized slab changed to denser eclogite facies as recorded by linear alkaline volcanism with strong mantle source (low La/Nb ratio) along the high Andes. Locally, transform fault subduction enhanced fracturing during slab bending permitting the tapping of undepleted mantle by these deep faults and causing trench parallel extension coeval with explosive subaqueous volcanism with strong OIB signature (low La/Nb ratio). Higher South Atlantic spreading rates than the trench normal convergence imparted the mechanism for trench rollback, thus enhancing the upper plate extensional deformation. Aptian increase in spreading rates coeval with protracted increase in the normal absolute plate motion terminated the active basement uplift; however, they persisted as submerged highs allowing the diachronous northsouth encroaching of the Cretaceous epeiric sea in along the Marañón and Ucayali basins. Prolonged Farallón Plate oblique convergence triggered strain partitioning and set-up important strike slip deformation such as the Tapacocha and Hormigas faults. Basin development involved pervasive transtensional deformation and tectonic segmentation and each one distinguished by its own stratigraphy, geochemistry, heat flow and subsidence history. Transtensional deformation involved deep crustal faults and complex lithosphere boudinage permitting important asthenospheric mantle de- compression melting magmatism that mixed with partially metasomatized subduction slab as documented by relative low La/Yb and La/Nb ratios and the occurrence of Nb-Ta negative anomalies. Two distinctive magmatic regimes are separated by an important and major plutonic regime linked to the emplacement of the Peruvian Costal Batholith (PCB) encompassing episodic multi-scale stopping, caldron subsidence and assimilation. The oldest volcanic regime (Casma Group), has higher mantle contribution and insignificant crustal contamination compare to the younger one (Quilmaná Formation). However, locally detrital zircons (DZ) and Hf isotopes support the presence of juvenile zircons supporting the absence of crustal contamination

SEIZMIČKO MODELIRANJE NA PODRUČJU OTOKA SUMATRE I NJEGOVE OKOLICE, INDONEZIJA, POMOĆU P-VALNE SEIZMIČKE TOMOGRAFIJE LOKALNIH I REGIONALNIH POTRESA

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.Otok Sumatra i njegova okolica, Indonezija, jedno su od najaktivnijih tektonskih područja na svijetu. Tamo se dogodio potres Aceh-Andaman, jedan od najrazornijih potresa na svijetu. Privukao je mnoge znanstvenike koji su u svojim istraživanjima primijenili različite metode, uključujući seizmičku tomografiju, kako bi razumjeli podzemnu strukturu i tektonski sustav otoka. Ova studija prva je koja prikazuje model podzemlja ispod otoka i njegove okolice koristeći se lokalno-regionalnim katalogom potresa iz seizmičke mreže Indonezijske agencije za meteorologiju, klimatologiju i geofiziku (BMKG). Tomografski model brzine P-valova (Vp), uspješno je razgraničio subduciranu ploču (velika brzina P-valova), zonu djelomičnoga taljenja (mali Vp), vulkanski luk (mali Vp) i rasjedne zone Sumatre (mali Vp). Odnos između subdukcijske zone i vulkanskoga luka na otoku može se vidjeti na nekoliko vertikalnih presjeka gdje se na dubini od oko 100 km javlja zona djelomičnoga taljenja koja služi kao izvor magme za neke vulkane na otoku. Model oceanske subducirane ploče također pokazuje izraženiji i strmiji nagib prema južnim regijama otoka Sumatre, što se vjerojatno može pripisati procesu starenja ploče u tome smjeru. Rezultati naglašavaju važnost BMKG seizmičke mreže u identifikaciji lokalno-regionalnih podzemnih struktura ispod indonezijskoga arhipelaga, posebno za glavne otoke kao što je Sumatra

Study of Seismicity Based on the Results of Hypocenter Relocation Using Double Difference (HypoDD) Method in West Sumatera and Its Surrounding

The presence of the Indo-Australian plate, the Eurasian plate and the active Sumatra fault zone makes the West Sumatra region and its surroundings have very high seismic activity. To describe the seismicity pattern, it is necessary to analyze the earthquake hypocenter relocation, one of which is using the double difference (hypoDD) method. This method basically uses the data residual travel time from each hypocenter pair to the earthquake seismic station. The purpose of this research is to analyze the relocation of the hypocenter and describe the seismicity pattern in the West Sumatra and surrounding areas. The data used in this study are the time arrivals of P and S waves during the period of  2022 obtained from the earthquake catalog at the Padang Panjang Geophysical Station. The results showed that the earthquake hypocenter was relocated 888 out of 934 earthquake events and the distribution of hypocenter relocation produces a good seismicity pattern. From the results of the earthquake hypocenter relocation, the seismicity pattern in the West Sumatra region and its surroundings is generally influenced by subduction zones and some due to active fault zones. Seismicity in the subduction zone and active faults of Sumatra has a depth of about 50 - 250 km and 5 - 20 km. This indicates that during the period of 2022, subduction zones with medium to deep depths are very active as well as in Sumatra's active fault zones, especially  in the Sianok segment

The Río Cañete Basin: Implications for the Mesozoic geoynamic evolution of the Peruvian margin

The evolution of the Río Cañete Basin provides a robust geodynamic model that can be extrapolated throughout the Peruvian margin. Transtensional crustal attenuation during the Jurassic early stages of Andean oblique subduction accounts for major crustal thinning and regional arc volcanism. Arrival of the lost “Chivaterous Plateau”, explains the termination of the Jurassic arc and development of a Neocomian shallow subduction and slab breakoff. Regional marine transgression was accompanied by patchy arc volcanism as well as localized subduction of an oceanic fracture. Protracted and persistent transtension supports the Albian/Cenomanian high rates of extension and upwelling of primitive mantle. The Jurassic calc-alkaline intra-arc is unbroken and displays different degrees of crustal contamination as documented in the Puente Piedra Group. Subduction slab input is displayed by the negative Nb and Ti anomaly. However, the LREE enrichment and moderately slope similar to the OIB contrast with the MREE and HREE gentler slope. The overall flattening and discrete HREE spoon shape suggest pyroxene and subordinate amphibole fractioning. Still, the negative Eu anomaly, and more siliceous magmatism in the south supports the significant feldspar fractioning and higher crustal contamination. Subduction Flattening during approach of an oceanic plateau triggered the abrupt collapsing and drowning of the Jurassic arc edifice and the sharp provenance change from a volcanic to a quartz rich basement source. Still, the timing and uplift of the Marañon Block and the Arequipa Massif, the synchronous subsidence between these basement uplifts, the Neocomian volcanic lull, and the restricted deposition of this Neocomian quartz rich clastic wedge west of the Marañon Block bolsters a Neocomian flat slab. The presence of 145-110 Ma alkaline to subalkaline basalts and andesites lavas along a linear belt west of the Marañon Block supports the slab breakoff. The chondrite normalized REE patterns amid OIB and EMORB, with almost flat HREE and almost absence of crustal contamination suggest amphibole and pyroxene fractioning. The continuous marine transgression is recorded by the shales and limestones of the Lima Group that terminated during Aptian times. The localized and anomalous subaqueous Pucusana Formation volcanism was associated with subduction of an oceanic fracture coeval with mantle upwelling. Indeed, the gently LREE and MREE slope and almost flat HREE chondrite normalized spider diagrams suggest pyroxene fractioning. The almost continuous transtension set up since the early Mesozoic triggered the large pull-apart basin developed during the Albian/Cenomanian. The basins thus developed, were characterized by variable crustal attenuation and subsidence and thick volcaniclastic deposition. The strong Nb negative anomaly in the Casma Group implied subduction slab input. But, the gentle and higher enrichment in LREE similar to OIB, and the almost flat HREE akin to EMORB and NMORB with and overall subtle Eu anomaly showed a significant contribution from undepleted mantle and important pyroxene fractionation

Origin of volatiles emitted by Plinian mafic eruptions of the Chikurachki volcano, Kurile arc, Russia : trace element, boron and sulphur isotope constraints

Author Posting. © The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Chemical Geology 478 (2018): 131-147, doi:10.1016/j.chemgeo.2017.10.009.Chikurachki is a 1816-m high stratovolcano on Paramushir Island, Kurile arc, Russia, which has repeatedly produced highly explosive eruptions of mafic composition. The present work is aimed at constraining the origin of volatile components (CO2, H2O, F, S, and Cl), along with B and S isotopic compositions in a series of phenocryst-hosted melt inclusions and groundmass glasses from basaltic andesite pyroclasts of the 1853, 1986, and prehistoric Plinian eruptions of the volcano. The ranges of volatile concentrations in melt inclusions (47–1580 μg/g CO2, 0.4–4.2 wt% H2O, 399–633 μg/g F, 619–3402 μg/g S and 805–1240 μg/g Cl) imply a sudden pressure release from ~ 460 through ~ 35 MPa that corresponds to ~ 1.2–16-km-depth range of magma ascent upon decompression. We conclude that rapid ascent of the volatile-rich basaltic magmas from ~ 16-km initial depth accompanied by near-surface bubble nucleation and growth, and subsequent magma fragmentation appear to be a primary reason for the Plinian character of the Chikurachki eruptions. Significant negative correlations of S with K, Zr, Nb, Ba, La, Ce, Pr (R = − 0.8 to − 0.9), no clear relationships of S with H2O, CO2 and Cl, but strong positive correlations of S/K2O with H2O/K2O, Cl/K2O and F/K2O preclude magma degassing to be the only process affecting volatile concentrations dissolved in the melt. The δ34S values of the studied inclusion and groundmass glasses range from − 1.6 to + 12.3‰, decrease with decreasing S, show significant positive correlations with H2O/K2O, Cl/K2O and F/Zr, and negative correlations with a number of incompatible trace elements. Neither open- nor close-system magma degassing can account for the observed range of δ34S. The δ11B values of the melt inclusions range from − 7.0 to + 2.4‰ with 13–23 μg/g B. The relationships of δ11B with B/K2O and B/Nb are inconsistent with magma contamination at shallow crustal depths. Linear character of 1/S vs. δ34S relationship suggests two-component mixing. The possible mixing end-members could be the magmas having similar major and trace element compositions, but strongly contrasting volatile contents and S isotopes. Based on the behaviour of fluid-mobile vs. fluid-immobile incompatible trace elements, we conclude that the subduction component likely represents a mixture of subduction sediment-derived melt with up to 60% of slab-derived fluid. Admixture of ~ 1–8% of the inferred subduction component to the depleted mantle wedge source is required to account for the compositional range of the Chikurachki melt inclusions, and ~ 0.4–10% to constrain the composition of Kurile arc mafic magmas.This work was benefited from the NENIMF financial support of AAG during his training as a SIMS research specialist, the NSF grant EAR 0911093 to AAG, and partially from the Russian Science Foundation grant #16-17-10145 to VSK and MEZ

NGHIÊN CỨU QUÁ TRÌNH TẠO MẪU PHỤC VỤ ĐO SÓNG ĐỊA CHẤN TRONG CÁC PHA NGẬM NƯỚC CÓ ÁP SUẤT VÀ NHIỆT ĐỘ CAO VỚI MÔ HÌNH ĐỚI HÚT CHÌM

Measurement elastic velocity of hydrous phases at high P-T of subduction slab by multi-anvil apparatusThe relationship between seismic wave propagation velocities and water content of hydrous rock has been identified by a study at Swiss Federal Institute of Technology Zurich (ETHZ). As a result, the Earth’s deep structure can be studied by combination of seismic tomography and petrological experiment. The result was achieved by applying ultrasonic techniques under ultra high temperature - pressure condition in multi-anvil apparatus. In this paper, the study is presented including the selection of represented samples, an important requirements for hydrous samples and their synthesis method that assure the sample quality suitable for the measurement of elastic velocity in condition corresponding with high P-T in subduction slab

The fluids’ geochemistry along the "Sperchios Basin - Northern Evoikos Gulf" Graben, a geodynamically complex area of Central Greece

The study area is a 130 km long fast spreading graben in Central Greece. Its complex geodynamical setting includes both the presence at depth of a subduction slab responsible for the recent (Quaternary) volcanic activity in the area and the western termination of a tectonic lineament of regional importance (the North-Anatolian fault). Its high geothermal gradient is evidenced by the presence of many thermal springs with temperatures from 19 to 82 C, issuing along the normal faults bordering the graben. In the period 2004-2012 about 50 gas and water samples have been collected and their chemical and isotopic analysis revealed a wide range of compositions. Going from west to east the gas composition changes from CH4- to CO2-dominated passing through mixed N2- CH4 and N2-CO2 compositions, while at the same time the He isotopic composition goes from typical crustal values (0.05 R/Ra) up to 0.87 R/Ra (corrected for air contamination), showing in the easternmost sites a small but significant mantle input. Isotopic composition of CH4-C indicates a thermogenic origin for the CH4-rich samples and hydrothermal origin for the remaining samples. Positive 15N values indicate a contribution of crustal derived nitrogen for the N2-rich samples. The 13C values of most the CO2-enriched samples show a mixed origin (mantle and marine carbonates). Also the chemical composition of the waters shows differences along the graben and two main groups can be separated. The first, represented by dilute waters (E.C. < 600 S/cm), is found in the westernmost sites characterised by the presence of CH4-rich and mixed N2-CH4 gases. The remaining waters display higher salinities (E.C. from 12 to 56 mS/cm) due to the mixing with a modified marine component. Only the water composition of easternmost sites in the Giggenbach’s cation triangular graph plots in the field of the partially equilibrated waters giving estimated temperatures at depth of 150-160 C.PublishedVienna, Austria4.5. Studi sul degassamento naturale e sui gas petroliferiope

Геодивайдер 102–103° в.д. в современной структуре литосферы Центральной Азии

A quasi-linear zone of noticeable geological and geophysical changes, which coincides approximately with 102–103° E meridians, is termed by the authors as “geodivider”. Active submeridional faults are observed predominantly along the zone and coincide with its strike. Seismicity is most intensive in the central part of this zone, from the Lake Baikal to the Three Rivers Region at the Sino-Myanmar frontier. Transects with deep seismic sections and energy dissipation graphs show most sharply increasing seismic energy amounts and hypocenter depths in the western part of the geodivider which delimits (in the first approximation) the Central Asian and East Asian transitional zones between the North Eurasian, Indian and Pacific lithosphere plates. The transpression tectonic regime dominates west of the geodivider under the influence of the Hindustan Indentor pressure, and the transtension regime prevails east of it due to the Pacific subduction slab submergence and continuation. The regime change coincides with an abrupt increase in the crust thickness – from 35–40 km to 45–70 km – west of the geodivider, as reflected in the geophysical fields and metallogenic characteristics of the crust. The direction of P- and S-waves anisotropy together with the GPS data show decoupling layers of the crust and mantle in the southern part of the geodivider. According to our investigations, the 102–103° E geodivider is a regional geological-geophysical border that may be compared with the Tornquist Line, and, by its scale, with the Uralian and Appalachian fronts and some others large structures.Квазилинейная зона заметных геологических и геофизических изменений совпадает приблизительно с меридианами 102–103° в.д. Активные субмеридиональные разломы развиты в этой зоне, названной авторами геодивайдером 102–103° в.д. Наиболее интенсивная сейсмичность характеризует центральную часть геодивайдера от озера Байкал до региона Трех рек на границе Китая и Мианмар. Проведение трансектов с глубинными сейсмическими разрезами и графиками диссипации сейсмической энергии показывает преимущественно резкое возрастание объемов сейсмической энергии и глубины гипоцентров на западном крыле геодивайдера. Геодивайдер разделяет, в первом приближении, Центрально-Азиатскую и Восточно-Азиатскую транзитные зоны между Северо-Евразийской, Индийской и Тихоокеанской литосферными плитами. Тектонический режим транспрессии преобладает к западу от геодивайдера под влиянием давления Индостанского индентора, и режим транстенсии распространен к востоку от него, благодаря глубокому погружению и продолжению Тихоокеанского слэба. Смена режимов совпадает с резким увеличением мощности коры к западу от геодивайдера от 35–40 до 45–70 км, отражающимся в геофизических полях и коровых металлогенических характеристиках. Направление P- и S-волн анизотропии наряду с данными GPS показывает их несовпадение в различных слоях коры и мантии в южной части геодивайдера. По результатам наших исследований геодивайдер 102–103° в.д. представляет собой тип геолого-геофизической границы, сопоставимой с линией Торнквиста, по масштабу с Уральским и Аппалачским фронтами и с рядом других крупных структур