Geodetic evidence for interconnectivity between Aira and Kirishima magmatic systems, Japan

It is not known whether clustered or aligned volcanic edifices at the Earth surface have connected magmatic systems at depth. Previously suggested by geological records of paired eruptions, volcano interconnectivity still lacks proper geodetic evidence. Here we use GPS time-series and deformation modeling to show how Aira caldera and Kirishima, two adjacent volcanic centers in Kagoshima graben (southern Japan), interacted during Kirishima unrest in 2011. Whereas Aira caldera had been inflating steadily for two decades, it deflated during the eruption of Kirishima which started with a large-volume lava extrusion. This deflation, which cannot be explained by stress changes, is interpreted as the result of magma withdrawal from the Aira system during the Kirishima replenishment phase. This study highlights the behavior of connected neighboring volcanic systems before and after a large eruption, and the importance of taking into account volcano interactions in eruption probability models

Magnetic character of a large continental transform : an aeromagnetic survey of the Dead Sea Fault

Author Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 8 (2007): Q07005, doi:10.1029/2007GC001582.New high-resolution airborne magnetic (HRAM) data along a 120-km-long section of the Dead Sea Transform in southern Jordan and Israel shed light on the shallow structure of the fault zone and on the kinematics of the plate boundary. Despite infrequent seismic activity and only intermittent surface exposure, the fault is delineated clearly on a map of the first vertical derivative of the magnetic intensity, indicating that the source of the magnetic anomaly is shallow. The fault is manifested by a 10–20 nT negative anomaly in areas where the fault cuts through magnetic basement and by a <5 nT positive anomaly in other areas. Modeling suggests that the shallow fault is several hundred meters wide, in agreement with other geophysical and geological observations. A magnetic expression is observed only along the active trace of the fault and may reflect alteration of magnetic minerals due to fault zone processes or groundwater flow. The general lack of surface expression of the fault may reflect the absence of surface rupture during earthquakes. The magnetic data also indicate that unlike the San Andreas Fault, the location of this part of the plate boundary was stable throughout its history. Magnetic anomalies also support a total left-lateral offset of 105–110 km along the plate boundary, as suggested by others. Finally, despite previous suggestions of transtensional motion along the Dead Sea Transform, we did not identify any igneous intrusions related to the activity of this fault segment.The project was funded by U.S.-AID Middle Eastern Regional Cooperation grant TA-MOU-01-M21-012

New approach to detect seismic surface waves in 1Hz-sampled GPS time series

Recently, co-seismic seismic source characterization based on GPS measurements has been completed in near- and far-field with remarkable results. However, the accuracy of the ground displacement measurement inferred from GPS phase residuals is still depending of the distribution of satellites in the sky. We test here a method, based on the double difference (DD) computations of Line of Sight (LOS), that allows detecting 3D co-seismic ground shaking. The DD method is a quasi-analytically free of most of intrinsic errors affecting GPS measurements. The seismic waves presented in this study produced DD amplitudes 4 and 7 times stronger than the background noise. The method is benchmarked using the GEONET GPS stations recording the Hokkaido Earthquake (2003 September 25th, Mw = 8.3)

The relationship between U.S. east coast sea level and the Atlantic meridional overturning circulation: A review

Scientific and societal interest in the relationship between the Atlantic Meridional Overturning Circulation (AMOC) and U.S. East Coast sea level has intensified over the past decade, largely due to (1) projected, and potentially ongoing, enhancement of sea level rise associated with AMOC weakening and (2) the potential for observations of U.S. East Coast sea level to inform reconstructions of North Atlantic circulation and climate. These implications have inspired a wealth of model‐ and observation‐based analyses. Here, we review this research, finding consistent support in numerical models for an antiphase relationship between AMOC strength and dynamic sea level. However, simulations exhibit substantial along‐coast and intermodel differences in the amplitude of AMOC‐associated dynamic sea level variability. Observational analyses focusing on shorter (generally less than decadal) timescales show robust relationships between some components of the North Atlantic large‐scale circulation and coastal sea level variability, but the causal relationships between different observational metrics, AMOC, and sea level are often unclear. We highlight the importance of existing and future research seeking to understand relationships between AMOC and its component currents, the role of ageostrophic processes near the coast, and the interplay of local and remote forcing. Such research will help reconcile the results of different numerical simulations with each other and with observations, inform the physical origins of covariability, and reveal the sensitivity of scaling relationships to forcing, timescale, and model representation. This information will, in turn, provide a more complete characterization of uncertainty in relevant relationships, leading to more robust reconstructions and projections

Thermochronometer record of central Andean Plateau growth, Bolivia (19.5°S)

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94850/1/tect1973.pd

A new class of transform plate boundary

The theory of plate tectonics postulates that the relative motion between two neighboring plates occurs along three types of boundaries: divergent (spreading center, rift), convergent (subduction, collision), and horizontal (transform). Because the theory assumes rigid behavior of plates, transform plate boundaries must lie along small circles around the pole of rotation of relative motion between two neighboring plates. However, global models of current plate motion (e.g., NUVEL-1A) show that several boundaries with significant horizontal motion (i.e., the Dead Sea Fault and the Eastern Andean Frontal Fault Zone) do not lie along small circles but rather intersect the circles at 45°. The orientation of these faults can be explained by a new theory of intraplate tectonics, which predicts the first-order intraplate stress field in terms of small circles, great circles, and spiral lines that intersect both sets of circles at 45°. According to the theory, these transform faults are situated along the 45° spiral lines and follow the direction of maximum horizontal shear stress. The theory also predicts that the direction of interseismic relative plate motion between the two plates should be oriented at 45° to the transform plate boundary; this prediction can be tested within a few years using space geodesy. The alignment of these faults along spiral lines is explained by the theory's predicted stress field and a plasticity (von Mises) yield stress criterion for earthquake rupture. It is suggested that these faults represent a new class of transform plate boundary between large deformable plates and not between rigid sub-plates, as formerly postulated

Kinematic modelling of large-scale structural asymmetry across the Dead Sea Rift

The Dead Sea Rift (DSR) is characterized by large-scale topographic and structural asymmetries: the rift's eastern side is flexed upward toward the axis and its overall shape resembles an uplifted shoulder; the western side of the rift is flexed down toward the axis and its overall shape resembles a wide arch. We use a kinematic model of the lithosphere to explain the cumulative deformation of the pre-rift topography in response to two tectonic processes: normal faulting due to lithospheric extension and isostatic uplift. The model considers the sum relief of three surfaces: relief that existed prior to the formation of the rift (initial topography), relief created by slip along a curved normal boundary fault (kinematic topography), and relief created by isostatic response of the lithosphere to this faulting and to an additional unmodelled load (isostatic topography). The model predicts the observed structure across the rift only when we considered a significant additional load, comparable in magnitude to the load induced by the kinematic topography. The additional load reflects the negative mass anomaly of the 8–10-km-deep Dead Sea Basin, which is filled with unconsolidated sediments. By constraining the model with the structural observations, we determined that the extension perpendicular to the rift axis lies in the range 1–4 km in the northern half of the rift and 2–8 km in the southern half. The model also explains other observations across the DSR, such as the configuration of the three present-day regional drainage systems and the observed low-magnitude upward deflection of the Moho beneath the rift