Jooyoung Eom

Surface mass balance contributions to acceleration of Antarctic ice mass loss during 2003–2013

Abstract Recent observations from satellite gravimetry (the Gravity Recovery and Climate Experiment (GRACE) mission) suggest an acceleration of ice mass loss from the Antarctic Ice Sheet (AIS). The contribution of surface mass balance changes (due to variable precipitation) is compared with GRACE‐derived mass loss acceleration by assessing the estimated contribution of snow mass from meteorological reanalysis data. We find that over much of the continent, the acceleration can be explained by precipitation anomalies. However, on the Antarctic Peninsula and other parts of West Antarctica, mass changes are not explained by precipitation and are likely associated with ice discharge rate increases. The total apparent GRACE acceleration over all of the AIS between 2003 and 2013 is −13.6 ± 7.2 Gt/yr2. Of this total, we find that the surface mass balance component is −8.2 ± 2.0 Gt/yr2. However, the GRACE estimate appears to contain errors arising from the atmospheric pressure fields used to remove air mass effects. The estimated acceleration error from this effect is about 9.8 ± 5.8 Gt/yr2. Correcting for this yields an ice discharge acceleration of −15.1 ± 6.5 Gt/yr2.

Correlated error reduction in GRACE data over Greenland using extended empirical orthogonal functions

Surface mass change estimates from Gravity Recovery and Climate Experiment (GRACE) spherical harmonic solutions are contaminated by North-South stripe noise due largely to aliasing of high frequency variations into monthly samples. These meridional stripes are especially troubling for ice mass balance studies of the Greenland Ice Sheet (GrIS) where large ice mass variations are known to occur along North-South trending coastlines. By assuming that mass variations and noise have different patterns in both space and time over Greenland, we use Extended Empirical Orthogonal Functions (EEOF) to filter out this noise. The method is compared with a conventional approach, by examining both continent-wide estimates, and regional changes. GRACE results are compared with independent regional estimates derived from a climate model. The EEOF filter is effective at separating ice mass change signals from meridional stripe noise, with better rejection of high temporal frequency noise and less signal attenuation and spatial smoothing compared to a conventional method. We use EEOF filtered GRACE data to examine regional seasonal variations. Consistent with surface and other data, results show ice mass loss along the West, South-West and East coasts during summer and gain in these regions during winter. In addition, there is summer ice mass gain in the central region of the GrIS.

Analysis of the Geological Structure of the Hwasan Caldera Using Potential Data

A geophysical mapping was performed for Hwasan caldera which is located in Euisung Sub-basin of the southeastern part of the Korean Peninsula. In order to overcome the limitation of the previous studies, remote sensing technic was used and dense potential data were obtained and analyzed. First, we analyzed geological lineament for target area using geological map, digital elevation model (DEM) data and satellite imagery. The results were greatly consistent with the previous studies, and showed that N-S and NW-SE direction are the most dominant one in target area. Second, based on the lineament analysis, highly dense gravity data were acquired in Euisung Sub-basin and an integrated interpretation considering air-born magnetic data was made to investigate the regional structure of the target area. The results of power spectrum analysis for the acquired potential data revealed that the subsurface of Euisung Sub-basin have two density discontinuities at about 1 km and 3-5 km depth. A 1 km depth discontinuity is thought as the depth of pyroclastic sedimentary rocks or igneous rocks which were intruded at the ring vent of Hwasan caldera, while a 3-5 km depth discontinuity seems to be associated with the depth of the basin basement. In addition, three-dimensional gravity inversion for the total area of Euisung Sub-basin was carried out, and the inversion results indicated two followings; 1) Cretaceous Palgongsan granite and Bulguksa intrusion rocks, which are located in southeastern part and northeastern part of Euisung Sub-basin, show two major low density anomalies, 2) pyroclastic rocks around Hwasan caldera also have lower density when compared with those of neighborhood regions and are extended to 1.5 km depth. However, a poor vertical resolution of potential survey makes it difficult to accurately delineate the detailed structure caldera which has a vertically developed characteristic in general. To overcome this limitation, integrated analysis was carried out using the magnetotelluric data on the corresponding area with potential data and we could obtain more reasonable geologic structure.

Detection of Long Period Seismic Events by Using a Portable Gravity Meter, gPhone

Abstract: A gravity meter has been used for exploring subsurface mineral resources and monitoring long-period eventssuch as Earth tides. Recently, researchers found several other intriguing features that we could even detect largeteleseismic earthquakes and monitor seismic ambient noise using gravimeters. The zero-length spring suspensiontechnology gives the gPhone (Micro-g LaCoste) excellent low frequency sensitivity, which may have implications forinvestigating much longer-period natural events (e.g., Earth’s hum, tsunami waves, etc.). In this study, we presentpreliminary results through temporary operation of the gPhone at Geumsan in South Korea for 9 months (Nov. 2008-Jul. 2009). The gPhone successfully recorded large teleseismic events and showed a clear seasonal variation of the Doublefrequency microseisms during its operation period.Keywords: gPhone, Teleseismic earthquake, Double frequency microseisms요약: 중력계는 주로 지하 광물자원 탐사 및 지구조석과 같은 장주기 이벤트를 관측하는데 사용되고 있다. 최근 연구자들은 이 중력계를 이용하여 대형 원거리 지진 및 지진상시잡음 관측과 같은 몇몇 새롭고 흥미로운 사실들을 발견하였다. Micro-g LaCoste사의 gPhone에 적용된 zero-length spring suspension 기술은 초저주파 신호도 훌륭히 관측 가능하게하며, 이는 Earth’s hum이나 심지어 대형 지진해일 등을 관측하는데 큰 도움을 줄 수 있음을 시사한다. 이 연구에서는 충남 금산에서 2008년 11월 부터 2009년 7월까지 9개월간 임시로 설치/운영하였던 gPhone 자료를 분석하여 원거리 대형지진관측 및 상시지진잡음의 계절적 변화에 관한 사전결과를 보고하고자 한다.주요어: gPhone, 원거리 지진, 상시지진잡음

Refinement of GRACE Gravity Model Including Earth's Mean Mass Variations

The Gravity Recovery and Climate Experiment (GRACE) has observed the Earths mass redistribution mainly caused by the variations of groundwater, ice sheet, and sea level since its launch in April 2002. The global gravity model estimated by the GRACE observation is corrected by barometric pressure, and thus represents the change of Earth mass on the Earths surface and below Earths surface excluding air mass. However, the total air mass varies due to the water exchange between the Earths surface and the atmosphere. As a result, the nominal GRACE gravity model should include the Earths gravity spectrum associated with the total air mass variations, degree 0 and order 0 coefficients of spherical harmonics ( C00). Because the water vapor content varies mainly on a seasonal time scale, a change of C00 ( δ C00) is particularly important to seasonal variations of sea level, and mass balance between northern and southern hemisphere. This result implies that δ C00 coefficients should be accounted for the examination of continental scale mass change possibly associated with the climate variations.

A Feasibility Study of AMT Application to Tidal Flat Sedimentary Layer

The marine seismic prospecting using a research vessel in the shallow sea near the coastal area has certain limits according to the water depth and survey environment. Also, for the electrical resistivity survey at seashore area, one may need a specially designed high-voltage source to penetrate the very conductive surface layer. Therefore, we have conducted a feasibility study on the application of magnetotelluric method (MT), a passive geophysical method, on investigating of shallow marine environment geology. Our study involves both theoretical modeling and field survey at the tidal flat area which represent the very shallow marine environment. We have applied the audio-frequency magnetotelluric (AMT) method to the intertidal deposits of Gunhung Bay, west coast of Korea, and analysed the field data both qualitatively and quantitatively to investigate the morphology and sedimentary stratigraphy of the tidal flat. The inversion of AMT data well reveals the upper sedimentary layer of Holocene intertidal sediments having a range of 13-20 m thickness and the erosional patterns at the unconformable contact boundary. However, the AMT inversion results tend to overestimate the depth of basement (30-50 m) when compared with the seismic section (27-33 m). Since MT responses are not significantly sensitive to the resistivity of middle layer or the depth of basement, the AMT inversion result for basement may have to be adjusted using the comparison with other geophysical information like seismic section or logging data if possible. But, the AMT method can be an effective alternative choice for investigating the seashore area to get important basic informations such as the depositional environment of the tidal flat, sea-water intrusion and the basement structure near the sea shore.