Tectonic geodesy revealing geodynamic complexity of the Indo-Burmese arc region, North East India

The plate boundary between India and Sunda plates across the Indo-Burmese arc (IBA) region is probably the most neglected domain as far as the plate motion, crustal deformation and earthquake occurrence processes are concerned. Because of the limited or no geodetic measurements across the IBA region, debate continues on the most appropriate plate boundary model for the region. Subduction along this boundary occurred in geological past, but whether it is still active is a debatable issue. It is believed that the predominantly northward India–Sunda relative plate motion of about 36 mm/year is partitioned between the Indo-Burmese wedge (IBW) and the Sagaing Fault (SF). However, it is not clear how relative plate motion between India and Sunda plates is accommodated across the IBA region – whether localized, partitioned or distributed, and in particular what is the slip rate and mode of slip accommodation across faults in the region? In such cases, Global Positioning System (GPS) measurements of crustal deformation have proved to be the best and probably the only tool. Our detailed seismo-tectonic study, crustal deformation study using high precision GPS measurements of eight years, strain rate estimates, field studies, analytical and finite element modelling of GPS data from the IBW region in North East India provide evidence for present-day active deformation front (or the plate boundary fault) between the India and Burma plates. On the basis of our extensive studies, it is now suggested that the Churachandpur–Mao Fault (CMF), a geologically older thrust fault, accommodates motion of about 16 mm/year through dextral strike–slip manner. The motion across the CMF constitutes about 43% of the relative plate motion of 36 mm/year between the India and Sunda plates. The remaining motion is accommodated at SF. On the basis of modelling, which suggests low friction along the CMF, absence of low-magnitude seismicity along the CMF, lack of historic and great and major earthquakes on the CMF and regions around it, and field studies, it is proposed that the motion across the CMF occurs predominantly in an aseismic manner. Such behaviour of the CMF significantly lowers the seismic hazard in the region

Seismicity modulation due to hydrological loading in a stable continental region: A case study from the Jektvik swarm sequence in Northern Norway

Seismic swarms have been observed for more than 40 yr along the coast of Nordland, Northern Norway. However, the detailed spatio-temporal evolution and mechanisms of these swarms have not yet been resolved due to the historically sparse seismic station coverage. An increased number of seismic stations now allows us to study a nearly decade-long sequence of swarms in the Jektvik area during the 2013–2021 time window. Our analysis resolves four major groups of seismic events, each consisting of several spatial clusters, that have distinct spatial and temporal behaviours. Computed focal mechanism solutions are predominantly normal with NNE–SSW strike direction reflecting a near-vertical maximum principal stress and a NW–SE near-horizontal minimum principal stress, which are controlled by local NW–SE extension. We attribute the swarms to fluid-saturated fracture zones that are reactivated due to this local extension. Over the time period, the activity tends to increase between February and May, which coincides with the late winter and beginning of spring time in Norway. We hypothesize that the seismicity is modulated seasonally by hydrological loading from snow accumulation. This transient hydrological load results in elastic deformation that is observed at local Global Navigation Satellite System stations. The loading is shown to promote failure in a critically stressed normal faulting system. Once a segment is activated, it can then also trigger neighboring segments via stress transfer. Our new results point to a close link between lithosphere and hydrosphere contributing to the occurrence of seismic swarm activity in northern Norway.publishedVersio

Preparations for future great earthquakes seen in levelling observations along two lines across the outer Himalaya

An important set of levelling observations across Central Nepal have been reported in the literature recently. We infer from these observations that recoverable elastic strains are accumulating in the upper crust of the region and will lead to a great earthquake in course of time. Limited levelling data from the Dehradun region in northwestern Himalaya show remarkable similarities to the Nepalese data and require a similar interpretation regarding preparation for the next great earthquake in the region

A glimpse of earthquake cycle in the Sumatra region

We analyse temporal variation of crustal deformation derived from Global Positioning System (GPS) measurement at SAMP, a permanent GPS site in Sumatra, Indonesia. The site is located at about 300 km from the epicentres of the giant 26 December 2004 Sumatra–Andaman (Mw 9.0–9.3) and the great 28 March 2005 Sumatra (Mw 8.6) earthquakes. It experienced an interseismic displacement at a rate of about 2 cm/yr towards east in the preceding four months of the 2004 earthquake. The 2004 and 2005 earthquakes caused coseismic displacements of about 15 cm towards west and about 18 cm towards southwest respectively. In the period between the two earthquakes and after the 2005 earthquake, slow transients arising due to postseismic deformation are clearly recorded at this site. The postseismic deformation is in the opposite sense to that of the interseismic deformation, indicating either relaxation of the lower crust and upper mantle or afterslip on the subduction interface that lies further downdip of the ruptured part of the subducting interface. The site also recorded probably a slow earthquake that occurred on 9 June 2005, which caused a westward movement of about 2 cm at SAMP. However, more data from other sites are required to further confirm and analyse this event. Together, these displacements provide a glimpse of crustal movement during the earthquake cycle in the region

Dynamic Relationship Study between the Observed Seismicity and Spatiotemporal Pattern of Lineament Changes in Palghar, North Maharashtra (India)

The Palghar region (north Maharashtra, India), located in the northwestern part of the stable continental region of India, experienced a low magnitude earthquake swarm, which was initiated in September 2018 and is continuing to date (as of October 2021). From December 2018 to December 2020, ~5000 earthquakes with magnitudes from M1.2 to M3.8 occurred in a small region of 20 × 10 km2. These earthquakes were probably triggered by fluid migration during seasonal rainfall. In this study, we have used multi-temporal Landsat satellite data of the year 2000, 2015, 2018, 2019, and 2020, extracted lineaments, and studied the changes in frequency and pattern of lineaments before and after the initiation of the swarm in the Palghar region. An increase in the lineament density and amount of rainfall are found to be associated with the increasing frequency of earthquakes

Gravity, GPS and geomagnetic data in India

Gravity, Global Positioning System (GPS) and Geomagnetic data sets in India are acquired by different research, academic and government institutions, under various projects. These data sets have extensively been utilized for natural resources and lithopsheric explorations, earthquake studies, atmospheric and ionospheric studies, control surveys, aircraft navigation, etc. The data are archived at individual institutions and have different modes of procurement considering some of the data, e.g., gravity data are classified in nature. Some of these data sets are contributed to the international observational network for example IGS and INTERMAGNET and are available as open source for the scientific communities. Present article provides information about different types of available Gravity, GPS and Geomagnetic data, their archival and mode of availability to the user community

Coulomb stress changes and aftershocks of recent Indian earthquakes

During the past decade remarkable progress has been made in studies related to fault interactions and how the occurrence of an earthquake perturbs the stress field in its neighbourhood, which may trigger aftershocks and subsequent earthquakes. These studies have significant implications on the seismic hazard assessment of a region, as the change in stress can cause either a delay or an advance in the occurrence of future earthquakes. Further, since the assessment of seismic hazard is dependent on the rupture parameters of past earthquakes, it is important to reliably estimate such parameters, viz. rupture location, geometry, and extent of past earthquakes. Here, we report the constraints on some of the rupture parameters of Indian earthquakes during the past 14 years, namely the 2001 Bhuj, 1999 Chamoli, 1997 Jabalpur, 1993 Killari and 1991 Uttarkashi earthquakes, which are derived using the available aftershock data and assuming that these aftershocks occurred in the zones of increased static stress. Analyses of teleseismic waveform of these earthquakes poorly constrained such parameters

Effect of Oral PUVAsol on the Quality of Life in Indian Patients Having Chronic Plaque Psoriasis

Background. Psoriasis is associated with a high impact on health-related QoL (quality of life). PUVAsol has been successfully used for treating psoriasis instead of standard PUVA therapy in developing countries. However, data for PUVAsol therapy and its effect on QoL in psoriatic patients is meagre. Objective. To investigate the effect of PUVAsol on the quality of life in patients having chronic plaque psoriasis. Materials and Methods. An observational prospective study done in patients having chronic plaque psoriasis. PASI and DLQI were calculated before initiating treatment with oral PUVAsol. These were compared with the respective scores after 12 weeks of regular treatment with PUVAsol. Statistical analysis was done using SPSS version 20.0. Results. Both PASI and DLQI showed statistically significant reduction after 12 weeks of regular treatment. 90% of patients responded favourably to PUVAsol therapy in the study and all the domains of DLQI showed significant reduction except domain of “work and school.” Conclusion. Our results show that regular PUVAsol treatment improves the physical appearance of disease as evident by decrease in PASI scores. It also improves the QoL of the patients. This study will add upon the growing evidence of efficacy of PUVAsol

Crustal deformation in the Indo-Burmese arc region: implications from the Myanmar and Southeast Asia GPS measurements

Several models of plate boundary and convergence between the Indian and South China plate across the Indo-Burmese arc (IBA) region have been proposed, which include active subduction, transform, oblique and no plate boundary. We theoretically compute the displacement fields corresponding to each model and compare them with the results of GPS measurements in Myanmar and Southeast Asia. Available GPS observations are consistent with the model in which relative plate motion of about 36 mm/yr between India and Sundaland is partitioned almost equally between the Sagaing fault and the IBA through episodic dextral motion. Eastward motion of the Indian plate is generally compensated by eastward motion of the South China plate. Thus almost no subduction occurs along the Indo-Burmese arc. The GPS data are consistent with strain accumulation in both regions