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Issue Title: CONT08 - Continuous geodetic VLBI Campaign 2008

The Earth Orientation Center of the International Earth Rotation and Reference Systems Service (IERS) has the task to provide the scientific community with the international reference time series of Earth orientation parameters (EOP), referred to as IERS EOP C04 or C04. These series result from a combination of operational EOP series derived from VLBI, GNSS, SLR, and DORIS. The C04 series were updated to provide EOP series consistent with the set of station coordinates of the ITRF 2014. The new C04, referred to as IERS EOP 14C04, is aligned onto the most recent versions of the conventional reference frames (ITRF 2014 and ICRF2). Additionally, the combination algorithm was revised to include an improved weighting of the intra-technique solutions. Over the period 2010–2015, differences to the IVS combination exhibit standard deviations of 40 μas for nutation and 10 μs for UT1. Differences to the IGS combination reveal a standard deviation of 30 μas for polar motion. The IERS EOP 14C04 was adopted by the IERS directing board as the IERS reference series by February 1, 2017.

Seafloor geodetic data from the Nankai Trough, off southwestern Japan, show that most offshore sites in this earthquake-prone region have high slip-deficit rates, revealing previously unknown locations that could be important for the mitigation of future earthquake- and tsunami-associated disasters. The Nankai Trough seismogenic zone Yusuke Yokota et al . have used seafloor geodetic observations to visualize the seismogenic zone along the Nankai Trough off southwestern Japan, which is thought to be one of the most dangerous megathrust zones in the world. They suggest that most offshore sites in this region have positive slip-deficit rates, revealing previously unknown locations that could be potential sources of future earthquakes and tsunamis. Low slip-deficit rates are observed in other regions, consistent with distributions of shallow slow earthquakes and subducting seamounts. Interplate megathrust earthquakes have inflicted catastrophic damage on human society. Such an earthquake is predicted to occur in the near future along the Nankai Trough off southwestern Japan—an economically active and densely populated area in which megathrust earthquakes have already occurred 1 , 2 , 3 , 4 , 5 . Megathrust earthquakes are the result of a plate-subduction mechanism and occur at slip-deficit regions (also known as ‘coupling’ regions) 6 , 7 , where friction prevents plates from slipping against each other and the accumulated energy is eventually released forcefully. Many studies have attempted to capture distributions of slip-deficit rates (SDRs) in order to predict earthquakes 8 , 9 , 10 . However, these studies could not obtain a complete view of the earthquake source region, because they had no seafloor geodetic data. The Hydrographic and Oceanographic Department of the Japan Coast Guard (JHOD) has been developing a precise and sustainable seafloor geodetic observation network 11 in this subduction zone to obtain information related to offshore SDRs. Here, we present seafloor geodetic observation data and an offshore interplate SDR-distribution model. Our data suggest that most offshore regions in this subduction zone have positive SDRs. Specifically, our observations indicate previously unknown regions of high SDR that will be important for tsunami disaster mitigation, and regions of low SDR that are consistent with distributions of shallow slow earthquakes and subducting seamounts. This is the first direct evidence that coupling conditions might be related to these seismological and geological phenomena. Our findings provide information for inferring megathrust earthquake scenarios and interpreting research on the Nankai Trough subduction zone.

In this paper we learn the new idea of forcing total outer independent edge geodetic number of a graph. Let G be a connected graph and R be a minimum total outer independent edge geodetic set of G. A subset L ⊆ R is known as a forcing subset for R if R is the unique minimum total outer independent edge geodetic set containing L. A forcing subset for R of minimum cardinality is a minimum forcing subset of R. The forcing total outer independent edge geodetic number of G denoted by f 1 t o i ( G ) is f 1 t o i ( G ) = min f 1 t o i ( R ) , where the minimum is taken over all minimum total outer independent edge geodetic set R in G. Some general properties satisfied by this concept are studied. It is shown that for any couple of integers l , m with0 < l ≤ m − 4, there exists a connected graph G such that f 1 t o i ( G ) = l and g 1 t o i ( G ) = m .

EGM2008 is a spherical harmonic model of the Earth's gravitational potential, developed by a least squares combination of the ITG‐GRACE03S gravitational model and its associated error covariance matrix, with the gravitational information obtained from a global set of area‐mean free‐air gravity anomalies defined on a 5 arc‐minute equiangular grid. This grid was formed by merging terrestrial, altimetry‐derived, and airborne gravity data. Over areas where only lower resolution gravity data were available, their spectral content was supplemented with gravitational information implied by the topography. EGM2008 is complete to degree and order 2159, and contains additional coefficients up to degree 2190 and order 2159. Over areas covered with high quality gravity data, the discrepancies between EGM2008 geoid undulations and independent GPS/Leveling values are on the order of ±5 to ±10 cm. EGM2008 vertical deflections over USA and Australia are within ±1.1 to ±1.3 arc‐seconds of independent astrogeodetic values. These results indicate that EGM2008 performs comparably with contemporary detailed regional geoid models. EGM2008 performs equally well with other GRACE‐based gravitational models in orbit computations. Over EGM96, EGM2008 represents improvement by a factor of six in resolution, and by factors of three to six in accuracy, depending on gravitational quantity and geographic area. EGM2008 represents a milestone and a new paradigm in global gravity field modeling, by demonstrating for the first time ever, that given accurate and detailed gravimetric data, asingle global model may satisfy the requirements of a very wide range of applications. Key Points Document the development of first ever gravity model to degree 2190 Demonstrate EGM2008's performance Compare EGM2008 with other models