Crustal Deformation of the Kendeng Fault Branches Area from GNSS and InSAR Data in Surabaya City, Indonesia

Slip rates on active faults derived from the interseismic velocity field are critical to understanding seismic hazards in metropolitan cities. This study integrated the data from the Global Navigation Satellite System (GNSS) and Interferometric Synthetic Aperture Radar (InSAR) to evaluate the interseismic velocities in the second-largest city in Indonesia, Surabaya, where branches of the Kendeng fault (the Surabaya and the Waru faults) pass through. Data from 16 campaign-mode GNSS stations collected between 2017 and 2020 from previous research are reprocessed to estimate the velocity field. Horizontal velocities under the ITRF frame range between -23.8 mm/yr and 47.9 mm/yr toward the southeast. Vertical velocities generally range between -1.3 mm/yr and -112.2 mm/yr. Sentinel-1A SAR data of both ascending and descending tracks acquired between November 2014 and July 2020 were used to generate the interferograms with the InSAR Scientific Computing Environment (ISCE) software. Furthermore, cumulative displacement time series were constructed using the Small BAseline Subset (SBAS) technique within the Generic InSAR Analysis Toolbox (GIAnT). This study also carried out the detection of outlier SAR epochs to improve the precision of Line-of-sight (LOS) velocity estimates. The LOS velocities range from -14.8 to 10.8 mm/yr in the ascending track and from -12.7 to 9.5 mm/yr in the descending track. These results will facilitate the detection of coupling behaviors on the Kendeng fault branches, which can improve our understanding of seismic risks in the Surabaya area.

Coseismic displacement interferences and patterns along subduction megathrusts: insights from analog modelling

<p>Finding a deformation pattern that is representative of a given stage of the seismic cycle of subduction megathrusts is crucial as this might provide clues about the upcoming earthquake. Here we focus on the short term interaction between seismic asperities and in particular on how geodetic velocities change in response to ruptures of an along-strike neighbor portion of the megathrust. Enhanced megathrust coupling, slab acceleration, in plane bending of the overriding plate, continental-scale viscoelastic mantle relaxation have been proposed as potentially responsible driving mechanisms. However, the paucity of observations from natural cases and the multiple- interrelated contributions that act at different spatial and temporal scales complicate the understanding of this process.</p><p>We use an analog model that simulates a series of laterally partial ruptures and analyze systematically the effect of slip episodes on deformation history of the neighbor “receiver” region. The analog model has the advantage of reproducing tens of seismic cycles with well controlled boundary conditions. The model shows that the deformation pattern associated to slip episodes has a characteristic twisting about a vertical axis. Such twisting interfere positively (causing velocity increase) or negatively (causing velocity decrease) with local interseismic velocity field depending on time since the last earthquake. Identifying accelerating or decelerating velocities in geodetic timeseries could be therefore informative of the seismic evolution of a subduction zone.</p>

The interseismic velocity field of the central Apennines from a dense GPS network

<p>Since 1999, we have repeatedly surveyed the central Apennines through a dense survey-style geodetic network, the Central Apennines Geodetic Network (CAGeoNet). CAGeoNet consists of 123 benchmarks distributed over an area of ca. 180 km × 130 km, from the Tyrrhenian coast to the Adriatic coast, with an average inter-site distance of 3 km to 5 km. The network is positioned across the main seismogenic structures of the region that are capable of generating destructive earthquakes. Here, we show the horizontal GPS velocity field of both CAGeoNet and continuous GPS stations in this region, as estimated from the position–time series in the time span from 1999 to 2007. We analyzed the data using both the Bernese and GAMIT software, rigorously combining the two solutions to obtain a validated result. Then, we analyzed the strain-rate field, which shows a region of extension along the axis of the Apennine chain, with values from 2 × 10<span>^–9</span> yr<span>^–1</span> to 66·× 10<span>^–9</span> yr<span>^–1</span>, and a relative minimum of ca. 20 × 10<span>^–9</span> yr<span>^–1</span> located in the L'Aquila basin area. Our velocity field represents an improved estimation of the ongoing elastic interseismic deformation of the central Apennines, and in particular relating to the area of the L'Aquila earthquake of April 6, 2009.</p>