Journal of Coastal Research 00 0 000–000 West Palm Beach, Florida Month 0000 Time Series Synthetic Aperture Radar Interferometry for Ground Deformation Monitoring over a Small Scale Tectonically Active Deltaic Environment (Mornos, Central Greece) www.cerf-jcr.org Issaak Parcharidis{, Penelope Kourkouli{, Efthimios Karymbalis{, Michael Foumelis{, and Vassilia Karathanassi{ {Harokopio University of Athens {National Technical University of Athens Department of Geography Laboratory of Remote Sensing El. Venizelou 70, 17671 Heroon Polytechniou 9, 15780 Athens, Greece Athens, Greece [email protected] [email protected] ABSTRACT PARCHARIDIS, I.; KOURKOULI, P.; KARYMBALIS, E.; FOUMELIS, M., AND KARATHANASSI, V., 0000, Time series synthetic aperture radar interferometry for ground deformation monitoring over a small scale tectonically active deltaic environment (Mornos, Central Greece). Journal of Coastal Research, 00(0), 000–000. West Palm Beach (Florida), ISSN 0749-0208. This study deals with the estimation of subtle ground deformation at millimetric accuracy over the broader area of the Mornos River delta in Central Greece and its spatio-temporal distribution for the period between 1992 and 2009 through Persistent Scatterers Interferometry (PSI). The results showed that the majority of the scatterers, which show subsidence, are located within the delta plain with mean subsidence rates throughout the delta varying between 27.2 and +0.7 mm/y. An attempt is made to highlight the geographic distribution, the amplitude, and the causes of the observed delta plain subsidence. The positive correlation between the thickness of the fine-grained Holocene deltaic deposits and the subsidence rates reveals that the main cause is the natural compaction of sediments. The highest subsidence is observed at Bouka Karahassani village, which corresponds to the area of the most recently abandoned river mouth, which is intensely eroded by marine processes. Apart from the dominance of fine sediments in the study area, subsidence may also be attributed to submarine gravitational mass movements along the steep slopes of the prodelta as well as to the reduction of sediment load after the dam construction in 1979. The NW part of the delta seems to have been affected by aseismic slip along a NE-SW trending normal fault buried beneath the alluvial deposits of the Skala torrent fan. ADDITIONAL INDEX WORDS: River Deltas, subsidence, Persistent Scatterers Interferometry, Mornos River Delta. INTRODUCTION The Permanent or Persistent Scatterers Interferometry (PSI) (Ferretti, Prati, and Rocca, 2001; Hanssen, 2005; Werner Repeat-pass interferometry is a unique tool for large-scale et al., 2003), a relatively recent development used to overcome monitoring (spatially continuous) of surface deformation at the previous limitations, is a technique implemented to a low cost (Massonnet et al., 1993; Zebker et al., 1994). calculate fine motions of individual points over wide areas Regardless of the applied differential interferometric method, covering mainly urban and semiurban environments (Burg- repeat-pass interferometry is limited by a number of param- mann et al., 2006; Colesanti et al., 2003; Parcharidis et al., eters, such as 2006; Raucoules et al., 2008; Salvi et al., 2004; Teatini et al., N large baselines, which lead to low correlation attributable 2005). The technique uses a series of coregistered Synthetic to spectral shift for distributed targets; Aperture Radar (SAR) scenes to identify time persistent N loss of coherence attributable to long temporal separation scatterer (PS) points. The processing is carried out on these between acquisitions; persistent points of the SAR images having stable radiometric N difficulties to unwrap interferograms with large baseline characteristics. By examining their interferometric phase it is attributable to low correlation and high fringe rates; and possible to monitor ground stability for an area that is normally N atmospheric artifacts attributable to tropospheric water characterized by its low coherence. Additionally millimetric vapor and ionospheric electron density. target displacement along the line of sight directions can be detected, allowing the measurement of slow terrain motion (Ferretti, Prati, and Rocca, 2001; Hanssen, 2005). DOI: 10.2112/JCOASTRES-D-11-00106.1 received 14 June 2011; The unique benefit of PS interferometry is its ability to accepted in revision 19 August 2011. Published Pre-print online XX Month XXXX. provide both annual average motion rates and deformation ’ Coastal Education & Research Foundation 2012 histories for the individual targets (Parcharidis et al., 2009). Journal of Coastal Research coas-28-05-09.3d 4/10/11 15:48:02 1 Cust # JCOASTRES-D-11-00106 0 Parcharidis et al. River deltas are coastal features developed from the accumu- States to analyze Late Holocene deposits and assess compac- lation of sediment near the mouth of rivers. They have been and tion rates. continue to be the heart of economic developments. They In Greece, Stiros (2001) studied the subsidence of the confront the coastal regions with dynamically changing Thessaloniki coastal plain, which composes part of the delta qualitative and quantitative characteristics of the river that complex of Axios, Aliakmon, Loudias, and Gallikos Rivers in feeds them. Pollution, canalization, urbanization, and defores- northern Greece for the time period between 1960 and 1999. He tation within the catchment areas affect the delta environ- proposed that the observed subsidence should be regarded as ment. The deltas themselves are protected areas and/or are the cumulative effect of several factors, including consolidation characterized by agricultural activity and in many cases by the of near-surface sediments attributable to the decline of the existence of urban centers. On tectonically active areas, delta piezometric level and the partial abandonment of the delta, evolution may be influenced by abrupt relative sea level oxidation of peat soils in the vadose zone, synsedimentary changes attributable mainly to coseismic uplift or subsidence deformation (faulting and flow), and loading-induced consoli- (Barnhardt and Sherrod, 2006). dation of deeper sediments. Land subsidence is a common phenomenon in modern delta Deltas with significant subsidence attributable to anthropo- plains because of compaction of sediments by consolidation of genic activities such as oil and gas extraction include the Niger, the dewatered material, compression of the load of the Magdalena, Makaham, MacKenzie, and Mississippi deltas subsequent overlain deposits, and groundwater or oil pumping (Ericson et al., 2006) and the Yellow River (Huanghe). Relative (Day et al., 1995; Dumont and El-Shabrawy, 2007; Meckel, Ten contributions of geologic and anthropogenic processes to Brink, and Williams, 2007; Nageswara Rao et al., 2010; Shi subsidence of river deltas or coastal plains are vigorously et al., 2007; Stanley, 2005). Previous studies on delta rivers debated. Shallow sediment compaction is often considered to be based on field data show that deformation features of the the dominant process (Meckel, Ten Brink, and Williams, 2007). hydrographic units are greatly related to hydrogeological Understanding the rate and the nature of subsidence of properties and ground–water–level variations. An identical sediment sequences in a delta is necessary for proper analysis hydrographic unit may exhibit different deformation features of the delta-building process through time. This is especially in different locations, and additionally the hydrogeology in the true in the present context of sea-level rise and coastal erosion. same location could exhibit different deformation in different The relative sea-level rise matters most in determining the periods or seasons (Shi et al., 2008; Wu et al., 2008). Except response of a deltaic coastal zone with subsiding areas being near coastal areas, land subsidence because of ground-water more susceptible to sea invasion (Mazzotti et al., 2009). Coastal pumping generally is not a serious hazard if the whole area subsidence of low-lying delta plains results in sea-level rise, subsides. The major problems related to subsidence areas are shoreline erosion, and wetland loss, which causes a threat to the potential destructive results caused by differential subsi- coastal populations (Jelgersma, 1996). Thus quantitative dence (Holzer and Pampeyan, 1981). understanding of subsidence is important for predicting Several studies were made on land subsidence from various relative sea-level rise, storm-surge flooding, and successful river deltas around the world. Cencini (1998) investigated the wetland restoration. subsiding Po delta in Italy, the greater part of which lies below The present paper concerns the application of PSI to detect sea level today. Stanley and Warne (1998) described and ground deformation in the Mornos delta for the period 1992– discussed symptoms of a destruction phase of the Nile delta in 2009. The objective of the study is three-fold: (i) detect spatial- Egypt during the past 150 years, triggered by water regulation temporal deformation of the delta, (ii) distinguish between that has disrupted the balance among sediment influx, erosive deformation attributable to natural delta sediment compaction and deformation induced by human activities, and (iii) effects of coastal processes, and subsidence. Becker and Sultan investigate the existence of differential vertical subsidence in (2009) evaluated the modern rates of subsidence