Plates & zones
The map shows where earthquakes happened. This is why they happen there — and where the North East sits, which is the part that matters most to anyone reading this from Assam.
What the boundary lines are
Switch Plate boundaries on in the map controls and the pattern in the markers stops being a pattern and becomes a diagram: almost every earthquake on the page sits on or beside one of these lines. They are Peter Bird’s PB2002 model, the standard open plate set, cut to about 1.1 km — finer than a plate boundary is actually known to, and finer than this map ever zooms.
Subduction zones are drawn heavier than the rest. That is where one plate is being forced under another, and it is where the largest earthquakes on Earth occur — the M 7.7 off Indonesia on this map is one of them. The lines are drawn in the one colour the severity scale does not use, so a boundary can never be mistaken for an event.
Why the North East shakes
The Indian plate is driving north into the Eurasian plate at roughly 5 cm a year — about as fast as a fingernail grows — and has been for some fifty million years. That collision built the Himalaya, and it has not stopped. In the North East the geometry is worse than a simple head-on push: the Indian plate is also being pushed under the Burma plate to the east, so the region is squeezed from two directions at once. The Shillong plateau, the Mishmi hills and the Naga thrust all belong to that argument.
This is why the region has produced two of the largest continental earthquakes ever recorded — Shillong in 1897 and Assam–Tibet in 1950, both around magnitude 8.6. The 1950 earthquake is not a distant fact for the flood module either: it raised the bed of the Brahmaputra, which is part of why the river floods the way it does now. The two halves of this site are describing one landscape.
India’s seismic zones
India is zoned II to V under IS 1893, the building code’s seismic map, where V is the most severe. The whole of Assam and almost all of the North East is Zone V — the same band as Kutch and the Andamans, and the highest the code defines. Guwahati, Dibrugarh, Jorhat, Silchar: all Zone V.
What that means in practice is about buildings, not about prediction. A zone is a design requirement — how much ground shaking a structure must be built to survive — and it says nothing about when. Nothing on this site predicts an earthquake, and the zoning does not either.
Where these come from
Plate boundaries: Bird, P. (2003), “An updated digital model of plate boundaries”, Geochemistry Geophysics Geosystems 4(3), 1027 — the PB2002 dataset, used here in its open GeoJSON form. The seismic zoning is IS 1893 (Part 1), published by the Bureau of Indian Standards; the historic earthquake magnitudes are the USGS and NGDC catalogue values, which for events of that age are estimates from felt reports and later analysis rather than instrumental readings.
The plate lines are geology, not a live feed. They do not change between one visit and the next, and nothing about them updates when the earthquake list does.