BMKG Flores InSAR Article Explains Method, Not Detailed Deformation Map

Labuan Bajo — — A magnitude-7.7 earthquake struck Flores, East Nusa Tenggara, on 15 August 2026, and Indonesia’s Meteorology, Climatology and Geophysics Agency (BMKG) has since released an initial report explaining how Interferometric Synthetic Aperture Radar (InSAR) is being used to map the event’s surface deformation. According to BMKG’s article on the Flores InSAR analysis, the method can provide spatial maps of ground deformation, but the publicly available text does not yet detail the specific satellite acquisitions or numerical displacement values for this earthquake.

The earthquake struck at 21:58:23 UTC on Friday, 14 August 2026, corresponding to 05:58:23 WITA on Saturday, 15 August 2026. BMKG reports a moment magnitude of 7.7, a focal depth of about 15 kilometres and an epicentre at 8.41° south and 121.39° east, offshore to the northeast of Nagekeo Regency in Flores. BMKG attributes the event to shallow thrust faulting on the Flores Back-Arc Thrust system, a north-dipping structure that accommodates convergence north of the Lesser Sunda Islands.

BMKG describes the Flores earthquake as destructive, noting casualties, damage and tsunami impacts across parts of East Nusa Tenggara and neighbouring provinces. A series of press releases and articles from the agency report tsunami observations at tide-gauge stations in NTT, West Nusa Tenggara, South Sulawesi and Southeast Sulawesi, and outline field survey results documenting run-up heights and inundation distances along the northern coast of Flores.

Separate national media coverage citing BMKG figures has also reported the large number of aftershocks recorded in the weeks following the mainshock.

How InSAR works

BMKG’s InSAR explainer on the Flores earthquake sets out the basic principles of the technique and its role in earthquake monitoring. Interferometric Synthetic Aperture Radar is a radar-based remote-sensing method that compares the phase of two synthetic-aperture radar (SAR) images acquired at different times and uses the difference to detect changes in the distance between the ground surface and the satellite sensor.

The resulting measurement is a displacement in the satellite’s line-of-sight, commonly abbreviated as LOS. BMKG notes that, under favourable conditions of data quality and surface characteristics, InSAR can reach centimetre- to millimetre-scale precision in quantifying this LOS displacement. LOS measurements, however, do not directly separate vertical uplift from horizontal motion: a single viewing geometry captures only the projection of the three-dimensional ground movement along the radar line-of-sight, and vegetation, water, steep topography and surface changes can reduce measurement reliability.

Unlike seismometers, which record shaking at specific sites, InSAR can provide spatially continuous maps of deformation over large areas without requiring physical instruments at every location. BMKG’s article emphasises that this capability makes the technique valuable for mapping earthquake-related ground deformation, volcanic deformation, subsidence and landslides, especially when access to affected areas is limited.

Scope of the Flores InSAR report

The Flores InSAR article published by BMKG on 25 August 2026 is described as an initial report on the use of radar data to analyse deformation from the 7.7-magnitude earthquake. The text explains that InSAR is being applied to quantify how the land surface moved during the event and notes that such deformation maps can help validate source models and support disaster mitigation.

However, the accessible narrative focuses on the methodology and general context rather than presenting a full numerical deformation map tied to named towns or islands. BMKG does not list, in the text, the specific satellite missions, acquisition dates before and after the earthquake, or detailed LOS displacement values at particular locations.

As a result, the article supports an explanation of what InSAR can do and how it is being used in principle for Flores, but it does not, on its own, substantiate claims that a particular village rose, subsided or shifted by a specific quantified amount.

How satellite data complements seismology

BMKG’s broader suite of publications on the Flores earthquake highlights how different data streams are being combined to understand the event. Seismological analyses provide parameters such as origin time, magnitude, depth and focal mechanism, and identify the Flores Back-Arc Thrust as the source of the mainshock. A separate kinematic source model article from BMKG describes a predominantly thrust mechanism with an east–west orientation typical of the Flores Thrust system.

InSAR-derived deformation maps answer a complementary question: how did the land surface move across the affected region. When radar data of sufficient quality are available, such maps can help researchers test whether the seismologically inferred fault slip is consistent with observed surface deformation and can guide the selection of priority areas for field surveys. BMKG’s reports on tsunami run-up, inundation distances and macroseismic intensity maps provide yet another layer of evidence about the earthquake’s impacts on communities and infrastructure.

None of these data sets alone—seismology, InSAR or tsunami and damage surveys—provides a complete assessment of the safety of individual buildings or slopes. BMKG’s communications stress the importance of integrating instrumental observations with field verification and engineering analysis to inform reconstruction and retrofitting after the Flores event. For residents and local authorities, satellite-based deformation analysis is one component of a wider hazard assessment framework that still relies on official safety guidance, structural inspections and direct observations on the ground.

Sources

• BMKG – Laporan Awal Analisis InSAR Gempa Flores 2026 M7.7
• Detikcom – BMKG Catat 14.993 Gempa Susulan Guncang Flores Sejak 15 Agustus; Okezone – Gempa Susulan Flores Capai 13.591 Aktivitas, Terbesar Berkekuatan M6,2