Search

The Magallanes‐Fagnano Fault is an active left‐lateral strike‐slip fault that cuts across Tierra del Fuego, forming the boundary between the South American and the Scotia plates. This fault may trigger strong earthquakes, as documented by the occurrence of two Mw ≥ 7.5 in December 1949. However, this region is characterized by one of the shortest historical archives in the world and by a growing population. The geological record is therefore needed in order to characterize the seismic information over a longer time scale and to improve the seismic hazard assessment. We conducted extensive field work, neotectonic mapping and excavated two paleoseismic trenches across one of the sharpest tectonic scarps in the Eastern onshore portion of the fault. Using scarp‐derived colluvial wedges, cross‐cutting relations, and 28 radiocarbon samples, we document evidences of at least six paleo‐earthquakes during the Holocene. Paleoseismic record is particularly accurate for the last two thousand years, for which period we determine an average recurrence interval of 1080 ± 150 years. For repeated earthquakes of same magnitude as the 1949 event, this recurrence interval is compatible both with the known geodetic and geomorphic slip rates. However, "paired earthquakes" in less than one or two centuries may also occur, suggesting that fault behavior could be characterized by irregular seismic cycles. Plain Language Summary: The Magallanes‐Fagnano Fault is a main active fault in Tierra del Fuego, at the southern tip of South America. This remote region has one of the shortest historical seismic record in the world. However, this fault may trigger strong earthquakes as occurred in 1949 and the surrounding population has been massively growing since. We therefore studied the paleo‐earthquake history of the fault to improve the seismic hazard assessment. We analyzed and dated the disrupted sediments in two trenches excavated across the fault to establish a paleo‐earthquake calendar. We document evidences of at least six paleo‐earthquakes during the last ten thousand years. Paleoseismic record is particularly accurate for the last two thousand years, for which period we determine a recurrence interval of 1080 +/− 150 years. However, "paired" major earthquakes in less than one or two centuries may also occur, suggesting that fault behavior could not be based on regular seismic cycles. Key Points: New records of at least six Holocene rupture events or phases in the eastern onshore portion of the Magallanes‐Fagnano FaultDuring the last two millennia, three major rupture events dated in a paleoseismological trench at 1949 CE, 860 ± 130 and at 2160 ± 170 cal yrs BPThe Magallanes‐Fagnano Fault may break in "paired earthquakes" separated by less than 1 or 2 centuries [ABSTRACT FROM AUTHOR]

Across the extreme south of Patagonia, the Magallanes‐Fagnano Fault (MFF) accommodates the left‐lateral relative motion between South America and Scotia plates. In this paper, we present an updated view of the geometry of the eastern portion of the MFF outcropping in Tierra del Fuego. We subdivide the MFF in eight segments on the basis of their deformation styles, using field mapping and interpretation of high‐resolution imagery. We quantify coseismic ruptures of the strongest recorded 1949, Mw7.5 earthquake, and determine its eastern termination. We recognize several co‐seismic offsets in man‐made features showing a sinistral shift up to 6.5 m, greater than previously estimated. Using 10Be cosmogenic nuclides depth profiles, we date a cumulated offset in post‐glacial morphologies and estimate the long‐term slip rate of the eastern MFF. We quantify a 6.4 ± 0.9 mm/a left‐lateral fault slip rate, which overlaps geodetic velocity and suggests stable fault behaviour since Pleistocene. [ABSTRACT FROM AUTHOR]

The Magallanes–Fagnano Fault is an active strike‐slip structure accommodating the relative displacement between South America and the Scotia Plate. The Chilean portion of the fault is poorly studied because most of it runs below the sea level in the Strait of Magellan. Our tectonic geomorphological study is focused on a rare onshore fault section, along which streams horizontally deflected by hundreds of metres since the last main deglaciation are compatible with a dominant left‐lateral fault kinematics and yield a slip rate of 15.7 ± 2.4 mm/year. This rate is between 2 and 3 times higher than the one estimated on the Argentinian portion of the fault over the same period. This spatial variation may be due to both glacial unloading on the fault zone and/or structural factors. These results point out the need to study strike‐slip faults on several portions to unravel behaviour changes related to internal or external forcing. [ABSTRACT FROM AUTHOR]

Background Liver macrophages are a heterogeneous cell population that produces factors involved in fibrogenesis and matrix turnover, including matrix metalloproteinase ( MMP) -9. During liver injury, their close proximity to hepatic progenitor cells and the ductular reaction may enable them to regulate liver repair and fibrosis. Aims To enumerate and characterise liver macrophages in patients with chronic hepatitis C, to determine whether a distinct population of macrophages is associated with the ductular reaction and portal fibrosis. Methods Immunostaining for macrophage markers ( CD68, CD163, CCR2), the ductular reaction (keratin-7) and MMP-9 was performed in liver biopsy sections from patients with chronic hepatitis C virus ( HCV) ( n = 85). Results Portal tracts were more densely populated with macrophages (10.5 ± 0.36 macrophages/HPF) than lobules (7.2 ± 0.16 macrophages/HPF, P < 0.001) and macrophages were found in close proximity to the ductular reaction. ≥30% of portal and periductal macrophages expressed MMP-9 and these were significantly associated with increasing stage of fibrosis ( rs = 0.58, 0.68, respectively, both P < 0.001). In contrast, MMP-9+ macrophages were largely absent in lobular regions and non-diseased liver. Hepatic MMP-9 mRNA levels and gelatinolytic activity were significantly associated with stage of fibrosis ( r s = 0.47, r s = 0.89, respectively, both P < 0.001). Furthermore, a second distinct CCR2+ macrophage population was localised to the centrilobular regions and was predominantly absent from portal and periductal areas. Conclusions These findings demonstrate significant regional differences in macrophage phenotypes, suggesting that there are at least two populations of liver macrophages. We propose that these populations have distinct contributions to the pathogenesis of chronic HCV-related liver disease. [ABSTRACT FROM AUTHOR]

Objective: 1) Assess the influence of word familiarity, phonological neighborhood, and acoustic patterns on speech audiometry variability. 2) Evaluate the interaction between those factors and patients' age and years of education. Method: Patients (n = 160) underwent otoscopy, tympanometry, pure‐tone, and speech audiometry. At an intensity level corresponding to a speech score between 40% and 60%, patients were presented 6 lists of 10 spondees, taken from a standard material used in France. Linguistic characteristics of the spondees and spectral acoustic patterns were characterized. PLS regression analysis was used to determine the factors influencing the percent score recognition for each word (PC). Results: PC varied from 18% to 92%. PC rose significantly with word familiarity (r = 0.38, P =. 005) and 1 kHz frequency band amplitude of each word's acoustic spectrum (r = 0.60, P =. 001). The percentage variability due to linguistic factors decreased significantly with age (from 30% below 50 years old to less than 10% above 60 years old), and with number of educational years (NEY; from 40% for NEY under 10 down to 18% for NEY above 10, for patients less than 50 years old). PC was significantly lower for spondees with large phonological neighborhood (F(1, 51) = 12, P =. 002), word familiarity being equal) for patients with NEY above 10. Conclusion: When taken independently from hearing loss, variability in PC was explained mostly by linguistic factors, combined with age and years of education, hence the need of carefully considering those factors when conceiving speech audiometry material. [ABSTRACT FROM AUTHOR]