Shallow depth, intensity of 4.0 led to intense tremors: National Center for Seismology

The epicentre, 10 km southwest of Red Fort, was well recorded by more than 30 broadband seismic stations installed by the National Center for Seismology.

An earthquake of 4.0 magnitude struck Delhi early Monday morning around 5:36 am, with its epicentre beneath Jheel Park in Dhaula Kuan, as an analysis by the National Center for Seismology (NCS) found that the sequence of events occurred along a northwest-southeast trending lineament.

Representational image.

The structural feature serves as a highly favourable location for the triggering of the main shock, primarily due to the significant structural heterogeneity present in and around the epicentral region, the report said.

The epicentre, 10 km southwest of Red Fort, was well recorded by more than 30 broadband seismic stations installed by NCS.

The variation in subsurface geological structures likely contributed to stress accumulation and subsequent rupture along this trend. An examination of past seismic activity within a 50 sqkm radius of the epicentre reveals that a magnitude 4.6 earthquake occurred south of the current epicentre on December 25, 2007, within a 6-km periphery of Monday’s earthquake.

“This suggests a normal pattern of seismogenesis in the past that corroborated with the seismic activity since 1990 in the region, highlighting the presence of pre-existing stress conditions and interactions among several lineaments and faults present in the area that may have influenced the recent event due to sub-surface heterogeneities of weaker category like association of source rock materials with fluids and water from the past riverine and acustrine formations beneath the source zone,” the report said.

The Jheel Park-Dhaula Kuan earthquake occurred due to normal faulting that supported the concept of hydro fracturing as the principal cause of seismogenesis of varying strengths.

Additionally, two well-known regional faults, the Mathura Fault and the Sohna Fault, are located in close proximity to the epicentre. Tremors of maximum intensity IV (MMI scale) in the epicentral region and minimum intensity III (MMI Scale) have been reported from a distance of around 0-15 km radius of the epicentre, respectively.

The report further stated that the shallow depth of the earthquake triggered a loud sound during the tremors when seismic waves reached the surface and interacted with air.

“The signature of today’s earthquake M4.0 is a good signature as the rock materials of source zone released energy prior to reaching its maximum credible past earthquake M4.6 of 2007 that occurred in the same epicentre source zone. The shaking is intense because of shallow depth of 5km and of intensity IV,” the report added.