• P SOLOMON RAJU

      Articles written in Journal of Earth System Science

    • Appraisal of Veldurti–Kalva–Gani (VKG) fault, Cuddapah Basin, India: Gravity and magnetic approach

      K SATISH KUMAR P SIVASANKAR S PARVEEN BEGUM B LAXMAN PHALKE MAHESH DEVIDAS V MAHA LAXMI NAIDU P SOLOMON RAJU D SRINAGESH

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      A ${\sim}$60 km long Veldurti–Kalva–Gani (VKG) fault is one of the identified strike-slip faults extending from Eastern Dharwar Craton (EDC) to Cuddapah basin in South Indian Shield. The recorded recent seismic activity during year 2012–2016 show occurrences of three microseismic events (<$M_{w}$ 2.0) in the vicinity of this fault. Historically, no major seismic events are recorded near this fault except magnitude of 5.0–5.9 (1843) earthquake at about ${\sim}$80 km west of this fault near Bellary. In the present study, analysis of available gravity, aeromagnetic and newly acquired ground gravity and magnetic data in the vicinity of the fault has been carried out to understand subsurface characteristics of this VKG fault and nearby structural features related to recent seismic activity. Analysis of aeromagnetic and gravity data shows shallow origin of the fault and earthquakes are associated with the zone of intersection like cross faults/lineaments which are parallel and perpendicular to the VKG fault. The calculated log normalized radially averaged power spectrum of the available gravity and aeromagnetic data shows four average depths $h_{0}$ (12.7 km), $h_{1}$ (6 km), $h_{2}$ (2.0 km) and $h_{3}$ (0.5 km). These estimated depths are possibly, bottom of the upper crust, thickness of the Cuddapah basin sediments, horizon of the basic sills, flows and the ferruginous quartzites and cumulative stratigraphic thickness of the Tadpatri shales and the Kurnools in the areas, respectively. The jointly inverted 2-D model from the ground gravity and aeromagnetic data along 2.7 km profile across VKG fault shows, faulting between Banganapalli Quartzite and Tadpatri Shales. The estimated average focal depth from the observed microseismic events is around 13 km. It is concluded from the present study that the observed microseismic events in the vicinity of VKG fault are associated with the intersection zones of cross faults/lineaments near the VKG fault and originated at an average depth of 13 km might be bottom of the upper crust. The estimated depths from the present analysis are well corroborated with previous geophysical studies.

      $\bf{Highlights}$

      $\bullet$ Mapping of Veldurti–Kalva–Gani fault through gravity, magnetic and aeromagnetic data which is associated with recent seismic activity.

      $\bullet$ Understanding of origin of the seismic activity through spectral analysis.

      $\bullet$ Estimation of depth to the basement, upper crust and thickness of Cuddapah basin sediments in the study region.

      $\bullet$ Estimation of focal depth from seismological data and corroboration with spectral analysis of gravity and aeromagnetic data.

    • A study of Palnadu earthquake sequence in the Cuddapah basin and its tectonic implications

      SRINAGESH D SUNILKUMAR T C NARESH B VITTHAL S DHIRAJ K SINGH RAVI P SINGH MAHALAXMI NAIDU G SURESH P SOLOMON RAJU V PAVAN KUMAR PRANTIK MANDAL A N S SARMA

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      On January 26, 2020, a moderate-sized earthquake ($M_{L}$ ${\sim}$ 4.6) located in the Palnadu sub-basin of Cuddapah basin was felt both in the states of Telangana and Andhra Pradesh. The earthquakes prior and after the $M_{L}$ 4.6 are located close to the thrust and along the periphery of the backwaters of the Pulichintala Reservoir. About 965 earthquakes in the magnitude range of 0.1–4.6 $M_{L}$ have been located by seismological network. The epicentral parameters obtained from double difference technique illuminated a steep seismogenic structure extending up to 8 km depth using a minimum 1-D velocity model. The b-value estimate is 0.82 for a completeness magnitude of $M_{c}$ 1.8 and could be associated with the intraplate event having a longer recurrence time. The focal mechanism solution obtained from waveform inversion reveals a pure double-couple mechanism of a strike-slip motion with a reverse component on a N–S trending focal plane. The spatial distribution of the earthquake sequence and fault plane solution of the main event are close to a thrust which is the most likely source region of the main-shock.

      $\bf{Highlights}$

      $\bullet$ Relocation of the Palnadu earthquake sequence illuminated a steep seismogenic structure extending up to 8 km depth.

      $\bullet$ The estimated lower b-value (0.82) could be associated with the intraplate event having a longer recurrence time.

      $\bullet$ The focal mechanism solution of the main-shock ($M_{L}$ 4.6) shows a strike-slip motion with a reverse component.

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