Scientists Map Marmara Sea Fault, Highlighting Impending Seismic Danger

The world's largest metropolises often form at tectonic plate boundaries, offering favorable terrain and sea access but creating constant disaster risks.

Photo: commons.wikimedia.org by Alexxx Malev, https://creativecommons.org/licenses/by-sa/3.0/

Galata Tower in Istanbul

3D Mapping Shows Epicenter Risks

Istanbul exemplifies this pattern. The city lies near the North Anatolian Fault, which slices across Turkey for 1,500 kilometers.

Historical observations show a concerning trend. Since 1939, a series of major earthquakes progressed from east to west, each rupture transferring energy to the next segment. In 1999, this chain reached Izmit at the eastern edge of the Marmara Sea, halting there. For over a quarter-century, seismologists have identified a "seismic gap"-tension continues to accumulate without release.

Forecasting is complicated by geography. Much of the fault lies beneath the Marmara Sea. On land, scientists use GPS and dense sensor networks to detect tiny ground shifts, but underwater measurements remain extremely difficult. Previously, the fault's location was known, but precise data on deep rock conditions were unavailable.

In a new study published in Geology, an international team presented the first detailed 3D scan of the Marmara Sea subsurface. They probed down to 40 kilometers and mapped which fault sections slide freely and which are locked, poised for rupture.

Electric Signals Replace Seismic Waves

To image the seafloor crust beneath water and sediment, researchers abandoned traditional seismic methods. Instead, they employed magnetotelluric surveying, which measures Earth's natural electromagnetic fields. Solar activity and ionospheric processes generate field fluctuations that penetrate deep rock layers, inducing weak electrical currents. How the rock conducts these currents reveals its composition and state.

Electrical resistance is the key metric. Dry, solid rock acts as an insulator, while fractured rock filled with salty water or geothermal fluids conducts electricity, signaling potential movement zones.

By deploying sensitive stations on the seabed, the team created a 3D map of "dry” and "wet” zones along the fault, offering crucial insights into earthquake mechanics.

Sliding and Locked Zones: Understanding Earthquake Mechanics

Tectonic plates move constantly. Near the Marmara Sea, this motion averages 20-25 millimeters per year, but it is uneven. Fault behavior depends on friction, influenced by fluid presence.

The study revealed complex vertical channels under the seabed. Low-resistance zones indicate fluids rising from the mantle, entering microscopic rock pores and cracks. Pressurized water reduces friction between plates, allowing slow, nearly imperceptible creep or minor tremors.

In contrast, high-resistance blocks are dry, solid, and locked. Friction here is maximal, preventing slip. Global plate motion compresses these locked areas like a spring, storing massive elastic energy. Over decades or centuries, this energy accumulates until the rock's strength is exceeded, resulting in sudden, powerful earthquakes.