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Recently, integrated geophysical‐geological surveys in the Nankai subduction zone in Japan have revealed that slow earthquakes repeatedly occur beneath the outer wedge of the forearc. During December 2020 to February 2021, clustered slow earthquakes propagated around the frontal thrust of the accretionary wedge. The frontal thrust ramps up from the basal décollement and slips over trench‐filling sediment along the landward edge of the Nankai trough floor. Here, the Paleo‐Zenisu ridge has been subducted beneath the inner‐outer slope border. In addition, ocean floor topography and geologic structure revealed by seismic reflection surveys completed before 2022 document that the basement of the Philippine Sea Plate beneath the frontal thrust has a seamount and a horst‐like basement high. The northern edge of the basement high is located at the ramp‐up position of the frontal thrust. The 2020–2021 clustered slow earthquakes started at the Paleo‐Zenisu ridge and propagated to the topographic highs beneath the deformation front. Considering that the relative plate convergence between the upper Amurian Plate of the Nankai forearc and the subducting Philippine Sea Plate is ∼6.0 cm/year, the basement high at the deformation front has uplifted the frontal crest of the wedge at an average rate of 2.7–5.7 mm/year for several tens to hundred thousand years. These rates are among some of the highest rock uplift rates measured in the world. The slow earthquakes in the off‐Kumano Nankai Trough in 2020–2021 are a snapshot of a "living" Nankai frontal thrust during the megathrust interseismic period. Plain Language Summary: Slow earthquakes family: slow slips, very low frequency earthquakes, and tremors are significant events for understanding the interseismic dynamics between large earthquakes along the convergent plate boundary in the ocean. Slow earthquakes took place during December 2020 to February 2021 in the Nankai Trough in Japan and propagated along the frontal edge of the upper plate. Seismic reflection surveys revealed that seamount‐like and horst‐like basement highs exist beneath the front, collide with the upper plate, and uplift trench filling sediments by a ramp thrust. Even the incipient plate boundary of the décollement is initiated within the sediments beneath the Nankai Trough. Such a deformation feature around the front is a source candidate for the slow earthquakes. The uplift rate of the frontal crest of the upper plate presents the same order of a few to several mm/year as that of the foreland of the Himalayan Mountain belt. The slow earthquakes in the off‐Kumano Nankai Trough in 2020–2021 appear the first snapshot of a "living" Nankai frontal thrust during inter‐large seismic period. Key Points: Between 2020 and 2021, slow earthquakes propagated around the frontal thrust of the accretionary wedge in the Nankai Trough off KumanoSeamount and horst‐like basement highs beneath the frontal thrust cause uplift and are associated with the slow earthquake eventsThe average uplift rate of the frontal crest is 2.7–5.7 mm/year, approximately the same order as that of the Himalayan foreland [ABSTRACT FROM AUTHOR]

Ryuji Ohashi,1 Yusuke Hosokawa,2 Go Kimura,3 Yukihiro Kondo,3 Keiji Tanaka,2 Shinichi Tsuchiya11Division of Diagnostic Pathology, 2Department of Intensive and Cardiac Care Unit, 3Department of Urology, Nippon Medical School, Tokyo, JapanAbstract: Disseminated intravascular coagulation (DIC) is the most frequent coagulation disorder in patients with prostate cancer. However, renal involvement in DIC associated with prostate cancer has rarely been documented. Herein, we present a case of metastatic prostate cancer presenting with acute renal failure (RF) triggered by DIC. An 80 year old man with metastatic prostate cancer was treated with antihormone therapy at an outpatient clinic. He was admitted to our hospital because of severe dyspnea and progressive RF. A hemorrhagic tendency was not clinically evident. Laboratory tests exhibited a significant coagulation disorder, suggestive of DIC. Despite treatment, his RF and dyspnea worsened, and he eventually passed away. An autopsy study revealed hypertensive nephrosclerosis superimposed by fibrin rich thrombi formation involving glomerular capillaries and arterioles characteristic of DIC. Additionally, focal segmental glomerulosclerosis was identified, which was presumably secondary to the glomerular endothelial and/or podocyte injury augmented by DIC. Those findings showed that glomerular injury, which was induced and subsequently exacerbated by DIC associated with prostate cancer, highly contributed to the progression of RF in our case. A differential diagnosis of DIC should be considered when a patient with prostate cancer presents with renal dysfunction.Keywords: disseminated intravascular coagulation, prostate cancer, renal pathology

The causes for forearc basin and megathrust rupture zone segmentation are controversial. The Nankai forearc, Japan, is separated into five domains based on topography: Enshu, Kumano, Muroto, Tosa, and Hyuga. The boundaries of these domains correspond to the rupture limits of large earthquakes. We examined the geologic structure of the boundary region between the Kumano and Muroto domains off the Kii Peninsula using multichannel seismic reflection data to evaluate the role of upper plate composition in controlling segmentation. The results suggest that thick cover sediments and underlying accretionary prism are obliquely thrust landward over the igneous basement complex rock in the region of offshore of Cape Shionomisaki and separate the forearc basin. The igneous basement complex rocks directly overlying the plate interface in the hypocentral regions of 1944 Tonankai and 1946 Nankai earthquakes. The 1944 earthquake originated at the base of the complex, and the rupture extent slipped past its basement boundary, whereas the 1946 event nucleated at the updip boundary of the basement complex. The dense igneous rocks might have worked as a heavily loaded barrier on the seismogenic megathrust and separated the rupture area of both the earthquakes. Upper plate geology may be an important factor in controlling seismogenesis in the Nankai Trough and may serve as an example for understanding the controls on megathrust slip in other subduction zones. Plain Language Summary: The Nankai Trough, Japan is the place where quakes nucleate in the margin and tsunamis repeatedly devastated circum‐Pacific societies. When, where, why, and how the quakes were started in the trench is a central scientific question but unsolved. The historical records of earthquakes suggest that the rupture started around Cape Shionomisaki of the Kii Peninsula, where there is also a topographic segment boundary of the ∼2,000 m deep basin in the middle continental slope. Our research of the geologic structure beneath the earthquake epicenters indicates a dense and hard rock mass situated upon the hypocenters of 1944, and 1946 megaquakes off Cape Shionomisaki. The rock mass might have worked as a heavy load and barrier on the low angle dipping plate boundary fault when the fault slipped the large rupture was propagated in the Nankai Trough. Key Points: The Nankai forearc basin is separated off the Kii Peninsula owing to the existence of middle Miocene igneous basement in the upper plateThe rupture areas of the 1944 Tonankai, 1946 Nankai, and 2016 off‐Mie earthquakes appear to be controlled by the igneous basementThe shallow distribution of very low‐frequency earthquakes and tremors are related to the geological heterogeneity of the upper plate [ABSTRACT FROM AUTHOR]

To investigate structural characteristics associated with variations in slip behavior on the plate boundary in the Nankai subduction zone, we conducted seismic reflection surveys in the central‐western Nankai Trough. Data were processed by pre‐stack depth migration. The resulting depth map of the top of the subducting Philippine Sea plate shows detailed topographic features of the plate boundary, including subducting seamounts and large‐scale undulations of the plate surface. We report the presence of a structurally anomalous region, potentially with low velocity, in the overriding plate at the boundary between the zone of large coseismic slip during the 1946 Nankai earthquake and the area producing slow earthquakes. This anomaly appears to be related to depth‐dependent variations in plate boundary slip style and plate coupling in the central‐western Nankai Trough. Plain Language Summary: The central‐western Nankai Trough off southwestern Japan is one of the best locations to study variations in slip style on the plate boundary fault in subduction zones because the fault slip distribution during the latest great earthquake, the distribution of slow earthquakes, and interplate coupling are known from previous studies. We conducted seismic surveys along densely distributed survey lines to image detailed subsurface structures in the central‐western Nankai Trough. A three‐dimensional map of the plate boundary fault geometry was created from seismic profiles used in this study. We found a structural anomaly, interpreted as a low‐velocity zone in the overriding plate, at the boundary between the slip zone of great earthquakes and the zone of slow earthquakes. This anomaly might be related to the variation of the plate boundary fault slip styles. Key Points: The topography of the subducting plate is mapped with densely spaced seismic profiles in the central‐western Nankai TroughAn arcuate structural anomaly in the overriding plate ∼100 km long with potentially low velocity coincides with the Tosabae TroughThe arcuate anomaly is located at the boundary between regions of strong and weak plate coupling [ABSTRACT FROM AUTHOR]

Fluid inclusions in crack-seal veins are analyzed in accreted melange now on land. The vein I inclusions are observed in the necked parts of sandstone blocks in melange, and the vein II inclusions developed in shale below the thrust fault, which cuts the melanges. The pressure and temperature estimations from the inclusions within vein I show that the cracks were sealed at ~125-195[degrees]C under ~92-144 MPa of fluid pressure. Vein II formed in cracks that might have opened in a damage zone caused by the thrust fault as it broke through, oceanic crust and into the damage; these veins contain fluid inclusions trapped at ~135-245[degrees]C under ~107-149 MPa of fluid pressure. The depth (~4-6 km below the seafloor) and temperature estimates are consistent with the conditions where an aseismic decollement within sedimentary rocks steps down into the oceanic basement, so that a thin section of oceanic crust underplates in the hanging wall. Such a step-down site is the updip limit of the seismogenic zone in the modern Nankai Trough. Keywords: melange, underplating, seismogenic zone, fluid inclusions, Shimanto belt.

Pseudotachylyte is present in the Shimanto accretionary complex in Shikoku, Japan. The pseudotachylyte occurs as a vein in a fault zone and displays flow structure, Ti[O.sub.2] microlites, and other melting-related textures. The mineral assemblage of the pseudotachylyte suggests that the temperature was raised at least 450 [degrees]C above the background levels in the host rocks. This is the first direct evidence of seismogenic fault rock from an accretionary complex. The pseudotachylyte-bearing fault is a roof thrust above under-thrusted melange, which is overlain by an offscraped package of coherent units. The geologic setting of the pseudotachylyte is consistent with melt generation during seismic slip along the master decollement in the subduction zone. Keywords: pseudotachylyte, accretionary complex, subduction, seismogenic zone, Shimanto.

Duplex structures several hundred metres thick bounded by marker beds exhibiting basalt-chert association have been found in the Franciscan complex near Pacheco Pass, central Diablo Range, California. The terrane was regionally metamorphosed and deformed under blueschist facies conditions at 150 [degrees]C and 7-8 kbar. Detailed mapping of the basalt-chert sequence has clarified the change of environment from mid-oceanic ridge to subduction zone. Eastward convergence of duplexing indicates eastward subduction of the oceanic plate during Early Cretaceous time. The presence of duplexing and a reconstruction of oceanic plate stratigraphy recorded within the underthrust unit demonstrate the accretionary origin of protoliths of the Franciscan coherent unit, which has long been believed to have an in situ origin, interpreted as either near-trench volcanism or accreted terranes in which 'geosynclinal-type' volcanism occurred.

Drilling during IODP NanTroSEIZE Expedition 316 led to the recovery of cores from the basal décollement in the frontal part of the Nankai accretionary prism and from a splay fault branching from the décollement at 25‐km landward of the prism toe. The core from the splay fault shows a main shear zone and two secondary shear zones. The main shear zone can be divided into two subzones. The upper subzone consists of a 1.2‐mm thick foliated gouge zone truncated downward by a through‐going fault encompassing a 0.4‐mm thick weakly foliated gouge interval. A nearby 200‐μm thick granular injection vein is interpreted as derived from the fault. The lower subzone consists of a foliated clayey gouge. A 70‐μm thick granular injection vein is also observed along this subzone. In the basal décollement core, microstructures consist of foliated gouge along a flat‐lying shear zone and seven flat‐lying or gently dipping secondary or incipient shear zones above. A redox front lies beneath the main shear zone. The shear zone and the redox front are truncated by a fault surface outlined by microbreccia developed at the expense of the overlying foliated gouge. Foliated gouge from the shear zones is tentatively interpreted as resulting from slow slip or aseismic creep. The weakly foliated gouge, the microbreccia, and the granular injection veins are interpreted as resulting from coseismic slip. The presence of the redox front beneath the main shear zone of the décollement fault core is interpreted as a consequence of oxidizing fluid flow along the microbreccia‐bearing fault. Plain Language Summary: To understand why some large subduction zone earthquakes are followed by destructive tsunamis and others are not is a key issue in seismic hazard assessment. Tsunami genesis is suspected to depend mainly on the capacity of faults in shallow parts of subduction zones to either transfer seismic slip from hypocentral depth upward or to dampen it before it reaches the surface. Expedition 316 of the IODP NanTroSEIZE program drilled across and retrieved cores from two major fault zones in the frontal part of the Nankai accretionary prism off Kii Peninsula. The rocks constituting the cored fault zones show microstructures which testify to both slow slip (plate tectonic steady‐state creep velocity or slow slip transient event velocity) and rapid slip (conventional earthquake slip velocity). It follows that in the Nankai Trough off Kii Peninsula, earthquake rupture can propagate along either of the major faults known there. Key Points: IODP Expedition 316 drilling across two fault zones in the Nankai accretionary prism allowed the recovery of intact cores of fault rocksFault rocks consist of microbreccia and weakly foliated gouge along sharp planar fault surfaces and foliated clayey gouge in millimeter‐thick shear zonesMicrobreccia and weakly foliated gouge suggest propagation of seismic slip along fault surfaces, while foliated gouge suggests aseismic or slow slip along shear zones [ABSTRACT FROM AUTHOR]

Research into the deformation process of the deeply buried Shimanto Belt in southwest Japan is presented. The fabric preserved in the tectonic melange has extensional thinning deformation because of shear along a decollement followed by posterior shortening and thickening caused by imbrication connected with underplating.

Accretionary complexes are believed to form via off scraping and underplating, leading to lateral and vertical growth. An important part of the accretionary process is the accretion of the upper oceanic crust and formation of melange. The link between formation of melange and duplexing in the Miyama Assemblage has been studied, with emphasis on its structure of a composite suite of duplexes, and systematic asymmetry.