Crustal deformation of Eastern Indonesia regions derived from 2010-2018 GNSS Data

Eastern Indonesia lies in a complex tectonic region due to the interaction of four major tectonic plates: the Australian Plate, Pacific Plate, Philippine Sea Plate, and Sunda Block. Therefore, this region hosted some destructive seismic activities as well as tectonic deformation, such as the Mw 7.5 Palu Earthquake, the sequences of the 2018 Lombok Earthquake, and the Mw 6.5 Ambon Earthquake in 2019. Our work proposes a recent study on crustal deformation in Eastern Indonesia inferred from Global Positioning System (GPS) velocity field. We used GPS data from the observations of 49 permanent and 61 campaign stations from 2010 to 2018. Here, our velocity field result represents long-term tectonic deformation regions in Eastern Indonesia continuously, from Bali in the west to Papua in the east, demonstrated both in the ITRF 2008 and the Sunda reference frames. The spatial pattern of velocity field map collected from this research will give an initial insight into the present-day tectonic condition in Eastern Indonesia and then can be used to improve our ability to assess this area’s earthquake potential.

Two Mechanisms of Earthquake-Induced Hydrochemical Variations in an Observation Well

Due to frequent large earthquakes in the Lanping-Simao fault basin—located in China’s Yunnan Province—the Simao observation well has observed groundwater discharge, as well as Ca2+, Mg2+, and HCO3− concentrations every day between 2001–2018. Over 18 years of observations, M ≥ 5.6 earthquakes within a radius of 380 km from the well were seen to cause hydrochemical variations. In this study, we investigated CO2 release and groundwater mixing as possible causes of regional earthquake precursors, which were caused by the characteristics of the regional structure, lithology, water-rock reactions, and a GPS velocity field. Precursory signals due to CO2 injection are normally short-term changes that take two months. However, groundwater mixing linked to earthquakes was found to take, at the earliest, 15 months. The proportion of shallow water that contributes to mixing was found to significantly increase gradually with the stronger regional strain. These finding delineate the two mechanisms of earthquake-induced hydrochemical variations in an observation well, and would contribute to a better understanding of chemical changes before events in the Simao basin.

Orogen-scale transpression accounts for GPS velocities and kinematic partitioning in the Southern Andes

The Southern Andes are regarded as a typical subduction orogen formed by oblique plate convergence. However, there is considerable uncertainty as to how deformation is kinematically partitioned in the upper plate. Here we use analogue experiments conducted in the MultiBox (Multifunctional analogue Box) apparatus to investigate dextral transpression in the Southern Andes between 34 °S and 42 °S. We find that transpression in our models is caused mainly by two prominent fault sets; transpression zone-parallel dextral oblique-slip thrust faults and sinistral oblique-slip reverse faults. The latter of these sets may be equivalent to northwest-striking faults which were believed to be pre-Andean in origin. We also model variable crustal strength in our experiments and find that stronger crust north of 37 °S and weaker crust to the south best reproduces the observed GPS velocity field. We propose that transpression in the Southern Andes is accommodated by distributed deformation rather than localized displacements on few margin-parallel faults.

Геодинамика территории Азербайджана на основе данных GPS за 2017–2019 гг.

the results obtained, in conjunction with these seismicity and the mechanisms of earthquakes, allow to determine the modern geodynamic situation of the studied region. The aim of the work was geodetic analysis and comparison of the results of GPS stations obtained for the period 2017-2019. on the territory of Azerbaijan. Methods. In the process of studying geodynamic processes using GPS technologies, two spatio-temporal modes are mainly used: a single redefinition of the initial coordinates of the points of geodetic networks and the displacement of the initial values of deformations. GPS data were processed using the GAMIT/GLOBK program. Results. One of the most pronounced features of the GPS velocity field is a decrease in the velocities of GPS stations (northern component of VN), perpendicular to the direction of expansion of the Greater Caucasus surface from south to north. The movement of the earth's surface to the north-north-east is interpreted as one of the reasons for this accumulation of stress.In addition, there is a tendency for horizontal movement in the Kura Depression and the Lesser Caucasus, which is reflected in the increase in velosity from west to east along the extension of the mountain range. It was determined that the earth's crust shortened at a velosity of ~ 5 mm / year in the Baku (Absheron peninsula). During 2019, on average, up to 8.4 mm per year in the north-northeast direction is observed for the territory of Azerbaijan. Separate velocities were also calculated for each station. Compared to 2018, it was determined that out of 24 GPS stations PQLG, XNQG, IMLG, QZXG, GANG, MNGG, FZLG, SATG, LKRG, LRKG and YRDG stations, the value of horizontal velocities increased by 0.5-7.0 mm/year, ZKTG, QBLG. At QSRG, ATGG, GDBG, AGDG, ALIG, JLVGG, GALG, GOBG and NDRG stations, the velocities values decreased by 0.5-3.1 mm/year. In 2019, the highest velocities were observed at Ganja, Mingachevir and Saatli stations. On average, velocities were 3.1-9.6 mm/year in the Greater Caucasus, 6.9-16.5 mm/year in the Kura Basin, 10.2-14.8 mm/year in the Talish area and on the Apsheron Peninsula. It varies between 3.6-4.8 mm/year. полученные результаты в совокупности с приведенной сейсмичностью и механизмами землетрясений позволяют определить современную геодинамическую ситуацию изучаемого региона. Целью работы являлся геодезический анализ и сравнение результатов GPS-станций, полученных за период 2017–2019 гг. на территории Азербайджана. Методы работы. В процессе изучения геодинамических процессов с использованием GPS технологий в основном применяются два пространственно-временных режима: однократное переопределение начальных координат точек геодезических сетей и смещение начальных значений деформаций. Данные GPS обрабатывали с помощью программы GAMIT/GLOBK. Результаты работы. Одной из наиболее ярко выраженных особенностей поля скорости GPS является уменьшение скоростей станций GPS (северный компонент VN), перпендикулярных направлению расширения поверхности Большого Кавказа с юга на север. Движение земной поверхности на север-северо-восток интерпретируется как одна из причин такого накопления напряжения. Кроме того, существует тенденция горизонтального движения в Курской впадине и на Малом Кавказе, что отражается в увеличение скорости с запада на восток по продолжению горного хребта. Было установлено, что земная кора сокращалась со скоростью ~ 5 мм/год в Баку (Апшеронский полуостров). В течение 2019 года в среднем по территории Азербайджана наблюдается до 8,4 мм в год в северо-северо-восточном направлении. Отдельные скорости были также рассчитаны для каждой станции. По сравнению с 2018 годом было определено, что из 24 GPS станций PQLG, XNQG, IMLG, QZXG, GANG, MNGG, FZLG, SATG, LKRG, LRKG и YRDG, значение горизонтальных скоростей увеличилось на 0,5–7,0 мм/год, ZKTG, QBLG. На станциях QSRG, ATGG, GDBG, AGDG, ALIG, JLVGG, GALG, GOBG и NDRG значения скоростей снизились на 0,5–3,1 мм/год. В 2019 году самые высокие скорости наблюдались на станциях Гянджа, Мингячевир и Саатлы. В среднем скорости составляли 3,1–9,6 мм/год на Большом Кавказе, 6,9–16,5 мм/год в бассейне Куры, 10,2–14,8 мм/год в Талышском районе и на Апшеронском полуострове. Колебания находятся в пределах 3,6–4,8 мм/год.

Isolating non-subduction-driven tectonic processes in Cascadia

Several tectonic processes combine to produce the crustal deformation observed across the Cascadia margin: (1) Cascadia subduction, (2) the northward propagation of the Mendocino Triple Junction (MTJ), (3) the translation of the Sierra Nevada–Great Valley (SNGV) block along the Eastern California Shear Zone–Walker Lane and, (3) extension in the northwestern Basin and Range, east of the Cascade Arc. The superposition of deformation associated with these processes produces the present-day GPS velocity field. North of ~ 45° N observed crustal displacements are consistent with inter-seismic subduction coupling. South of ~ 45° N, NNW-directed crustal shortening produced by the Mendocino crustal conveyor (MCC) and deformation associated with SNGV-block motion overprint the NE-directed Cascadia subduction coupling signal. Embedded in this overall pattern of crustal deformation is the rigid translation of the Klamath terrane, bounded on its north and west by localized zones of deformation. Since the MCC and SNGV processes migrate northward, their impact on the crustal deformation in southern Cascadia is a relatively recent phenomenon, since ~ 2 –3 Ma.

New geodetic constraints on southern San Andreas fault-slip rates, San Gorgonio Pass, California

Assessing fault-slip rates in diffuse plate boundary systems such as the San Andreas fault in southern California is critical both to characterize seis­mic hazards and to understand how different fault strands work together to accommodate plate boundary motion. In places such as San Gorgonio Pass, the geometric complexity of numerous fault strands interacting in a small area adds an extra obstacle to understanding the rupture potential and behavior of each individual fault. To better understand partitioning of fault-slip rates in this region, we build a new set of elastic fault-block models that test 16 different model fault geometries for the area. These models build on previ­ous studies by incorporating updated campaign GPS measurements from the San Bernardino Mountains and Eastern Transverse Ranges into a newly calculated GPS velocity field that has been removed of long- and short-term postseismic displacements from 12 past large-magnitude earthquakes to estimate model fault-slip rates. Using this postseismic-reduced GPS velocity field produces a best- fitting model geometry that resolves the long-standing geologic-geodetic slip-rate discrepancy in the Eastern California shear zone when off-fault deformation is taken into account, yielding a summed slip rate of 7.2 ± 2.8 mm/yr. Our models indicate that two active strands of the San Andreas system in San Gorgonio Pass are needed to produce sufficiently low geodetic dextral slip rates to match geologic observations. Lastly, results suggest that postseismic deformation may have more of a role to play in affecting the loading of faults in southern California than previously thought.

Present GPS velocity field along 1999 Izmit rupture zone: evidence for continuing afterslip 20 yr after the earthquake

SUMMARY In order to better assess earthquake hazards, it is vital to have a better understanding of the spatial and temporal characteristics of fault creep that occur on ruptured faults during the period following major earthquakes. Towards this end, we use new far-field GPS velocities from continuous stations (extending ∼50–70 km from the fault) and updated near-fault GPS survey observations, with high temporal and spatial density, to constrain active deformation along the Mw7.4, 1999 Izmit, Turkey Earthquake fault. We interpret and model deformation as resulting from post-seismic afterslip on the coseismic fault. In the broadest sense, our results demonstrate that logarithmically decaying post-seismic afterslip continues at a significant level 20 yr following 1999 Earthquake. Elastic models indicate substantially shallower apparent locking depths at present than prior to the 1999 Earthquake, consistent with continuing afterslip on the coseismic fault at depth. High-density, near-fault GPS observations indicate shallow creep on the upper 1–2 km of the coseismic fault, with variable rates, the highest and most clearly defined of which reach ∼12 mm yr−1 (10–15 mm yr−1, 95 per cent c.i.) near the epicentre between 2014–2016. This amounts to ∼half the long-term slip deficit rate.

How Has GPS Velocity Field Changed Along the 1999 Izmit Rupture 20 Years After the 1999 Izmit, Turkey Earthquake?

<p>A seismic gap along the western segment of the North Anatolian Fault, in the Marmara-Izmit region, was identified before the 1999 M7.6, Izmit and M7.4 Duzce earthquakes, so the region along the coseismic fault has been monitored with geodetic techniques for decades, providing well defined pre-, co- and post-seismic deformations. Here, we report new continuous and survey GPS measurements with near-fault (~2 – 10 km to the fault) and far-fault (~50 – 70 km from the fault) stations, including 7 years (2013 – 2019) of continuous observations, and 5 near-fault campaigns (every six months between 2014 – 2016) to further investigate postseismic deformation. GPS observations were processed with the GAMIT/GLOBK (v10.7) GNSS software. We used these observations to estimate the spatial distribution of current aseismic after-slip, along the 1999 Izmit rupture. We also searched for spatiotemporal changes of shallow creep events along the surface trace. With elastic models and GPS observations, we determined a shallow creep rate that reaches a maximum around the epicenter of the 1999 Izmit earthquake of about 12.7 ± 1.2 mm/yr, consistent with published InSAR results. Creep rates decrease both east and west of the epicentral region. Moreover, we show that broad-scale postseismic effects that diminish logarithmically, continue at present. (This study is supported by TUBITAK 1001 project no: 113Y102 and 117Y278)</p>

Kinematics and deformation of the southern Red Sea region from GPS observations

SUMMARY The present-day tectonics of the southern Red Sea region is complicated by the presence of the overlapping Afar and southern Red Sea rifts as well as the uncertain kinematics and extent of the Danakil block in between. Here we combine up to 16 yr of GPS observations and show that the coherent rotation of the Danakil block is well described by a Danakil-Nubia Euler pole at 16.36°N, 39.96°E with a rotation rate of 2.83 deg Myr–1. The kinematic block modeling also indicates that the Danakil block is significantly smaller than previously suggested, extending only to Hanish-Zukur Islands (∼13.8°N) with the area to the south of the islands being a part of the Arabian Plate. In addition, the GPS velocity field reveals a wide inter-rifting deformation zone across the northern Danakil-Afar rift with ∼5.6 mm yr–1 of east–west opening across Gulf of Zula in Eritrea. Together the results redefine some of the plate boundaries in the region and show how the extension in the southern Red Sea gradually moves over to the Danakil-Afar rift.

Anassessment of GIA solutions based on high-precision GNSS velocity field for Antarctica

Past mass loads, especially LGM (Last Glacial Maximum), may cause the viscoelastic response of the Earth, this phenomenon is the so-called glacial isostatic adjustment (GIA). GIA not only includes the horizontal and vertical motions of the crust but also the shape, the gravity field and rotation axis of the earth. Due to the uncertainties in the ice loading history and the mantle viscosity, modeling GIA will be difficult and challenging in Antarctica. The GPS velocity field provides an effective method to constrain the GIA vertical velocity; however, to obtain the high-precision GPS velocity field, we must consider the effects of common mode error(CME) and the choice of optimal noise model (ONM). We used independent component analysis(ICA) to remove the CME recorded at 79 GPS stations in Antarctica and determined the ONM of GPS time series based on the Akaike information criterion (AIC). Then, the high-precision GPS velocity field is obtained; we used the high-precision GPS velocity field to assess the application of GIA models in Antarctica. The results show that the maximal GPS velocity variation is up to 1.15 mm yr−1, and the mean variation is 0.18 mm yr−1. We find systematic underestimations of all GIA model velocities in the Amundsen Sea area (ASE). In the north Antarctic Peninsula (NAP), the vertical velocities are underestimated by 6 GIA models but not the WANG model. Because the upper mantle viscosities in the NAP are lower than those in the south Antarctic Peninsula (SAP),the GPS vertical velocities in NAP regions are larger than SAP regions. In the Filscher-Ronne Ice Shelves (FRIS), the observed GPS velocity and predicted GIA model velocity are consistent. In East Antarctica (EA), the vertical motion is nonsignificant, and the GIA and ice loading have a small impact in this area.