Earthquakes originate from the sudden release of elastic strain energy accumulated along tectonic fault planes, propagating through Earth's interior and lithosphere as seismic wave trains. The subterranean initiation point where rupture commences is designated as the hypocenter or focus, while the point vertically above it on the surface constitutes the epicenter. Seismology classifies seismic waves into body waves and surface waves. Primary (P) waves are compressional longitudinal waves capable of traversing solid, liquid, and gaseous media at velocities between five and eight kilometers per second. Secondary (S) waves are shear transverse waves that propagate strictly through solid materials, creating a pronounced seismic shadow zone between 103 degrees and 142 degrees from the epicenter, which historically proved the liquid state of the outer core. Surface waves, encompassing Rayleigh and Love waves, generate the greatest ground displacement and infrastructural destruction. Earthquake quantification relies on two distinct parameters: the logarithmic Richter and Moment Magnitude (Mw) scales measuring released seismic energy, and the qualitative Modified Mercalli Intensity (MMI) scale evaluating visible surface destruction from Roman numerals I to XII. In India, seismic hazard zonation mapped by the Bureau of Indian Standards (IS 1893) delineates four distinct risk categories ranging from Zone II to Zone V.
High-yield conceptual summaries for competitive exams and rapid revision.
The hypocenter (focus) is the exact sub-surface point of fault rupture, whereas the epicenter is the surface point directly perpendicular above the hypocenter.
P-waves (Primary waves) are longitudinal compressional waves that travel fastest and can propagate through solids, liquids, and gases.
S-waves (Secondary waves) are transverse shear waves that travel only through solids, failing to propagate through Earth's liquid outer core.
The S-wave shadow zone extends from 103 degrees to 180 degrees from an earthquake epicenter, confirming the liquid nature of Earth's outer core.
The P-wave shadow zone forms a band between 103 degrees and 142 degrees from the epicenter due to refraction at the mantle-core boundary.
Rayleigh waves induce elliptical retrograde ground motion, while Love waves generate horizontal shearing perpendicular to the wave propagation direction.
Surface waves travel slower than body waves but produce the largest amplitudes and inflict the highest degree of structural damage during quakes.
The Richter scale is an open-ended base-10 logarithmic scale where each whole number increase represents a ten-fold increase in measured wave amplitude.
Each unit increment on the Richter magnitude scale corresponds to an approximate 31.6-fold (or 10^1.5) increase in the total seismic energy released.
The Modified Mercalli Intensity (MMI) scale is a qualitative scale ranking observed structural shaking and human perceptibility from I (not felt) to XII (total damage).
Seismometers utilize the principle of inertia of a suspended mass to detect and record seismic ground displacements as seismograms.
The Indian subcontinent is divided into four seismic zones by IS 1893: Zone II (low risk), Zone III (moderate), Zone IV (severe), and Zone V (very severe).
Zone V encompasses the entire northeastern region of India, parts of Jammu & Kashmir, Himachal Pradesh, Uttarakhand, the Rann of Kutch, and Andaman & Nicobar.
The San Andreas Fault in California is a prominent dextral (right-lateral) strike-slip transform fault separating the Pacific and North American plates.
Benioff-Wadati zones are inclined planar zones of seismicity corresponding to the downgoing slab in oceanic-continental or oceanic-oceanic subduction boundaries.
hardEarthquake Seismic Zones, BIS Codes & Tsunamis
The deadly 1993 Latur (Killari) earthquake in Maharashtra was significant in Indian seismology because it revealed high seismic vulnerability in which geologic setting?
Verified Explanation
The 30 September 1993 Killari (Latur) earthquake (Mw 6.2) occurred within the peninsular shield, which was historically categorized as a seismically stable continental region (Zone I). This event led to the re-evaluation of peninsular seismic hazard and the elimination of Zone I in Indian codes.
2ID: GK-DMGT-00119
mediumEarthquake Seismic Zones, BIS Codes & Tsunamis
In October 2005, a devastating earthquake of magnitude Mw 7.6 struck near Muzaffarabad and caused severe casualties in Jammu & Kashmir. Along which geological fault structure did this rupture occur?
Verified Explanation
The 2005 Kashmir earthquake (Mw 7.6) was caused by a major rupture along the Balakot-Bagh Fault in the sub-Himalayan northwest syntaxial bend. It caused massive landslides, building collapses, and killed over 80,000 people across the region.
3ID: GK-DMGT-00122
mediumEarthquake Seismic Zones, BIS Codes & Tsunamis
Which premier engineering institute in India developed and deployed the early regional Earthquake Early Warning (EEW) system in Uttarakhand using real-time seismic sensor telemetry?
Verified Explanation
The Department of Earthquake Engineering at IIT Roorkee, funded by the Uttarakhand State Disaster Management Authority (USDMA), designed and operationalized the Uttarakhand Earthquake Early Warning System (UEEWS) with sensor networks providing critical seconds of advance alert based on P-wave detection.
4ID: GK-DMGT-00124
hardEarthquake Seismic Zones, BIS Codes & Tsunamis
In August 1950, which colossal earthquake with a magnitude of Mw 8.6 struck the Assam-Tibet border region, causing massive river damming and altering the course of the Brahmaputra River?
Verified Explanation
The 1950 Assam-Tibet earthquake (Mw 8.6) is the largest recorded instrumented intra-continental collision earthquake in the Himalayas. It generated massive rockslides that dammed the Subansiri and Dihang rivers; their subsequent breaches unleashed catastrophic secondary floods across Upper Assam.
5ID: GK-DMGT-00129
hardEarthquake Seismic Zones, BIS Codes & Tsunamis
Why did the 1897 Great Shillong Plateau Earthquake (Mw ~8.1) become a landmark event in global seismology studied by R.D. Oldham?
Verified Explanation
Richard Dixon Oldham's seminal 1899 memoir on the 1897 Assam (Shillong) earthquake analyzed seismograms from worldwide stations, establishing the first empirical proof that earthquake vibrations propagate as three distinct wave types: primary (P), secondary (S), and surface waves.
6ID: GK-DMGT-00296
easyEarthquake Seismic Zones, BIS Codes & Tsunamis
Which mobile application was developed by the National Centre for Seismology (NCS) to provide instant real-time earthquake epicentre and magnitude alerts to citizens?
Verified Explanation
The 'BhooKamp' mobile application was launched by the National Centre for Seismology (NCS), Ministry of Earth Sciences. It disseminates real-time earthquake parameters (origin time, epicentre, depth, magnitude) to citizens and disaster managers across India.
7ID: GK-DMGT-00300
mediumEarthquake Seismic Zones, BIS Codes & Tsunamis
The devastating 1993 Killari earthquake in Maharashtra (Magnitude 6.2) was classified as what type of unusual seismic event occurring within a stable intraplate region?
Verified Explanation
The September 30, 1993 Killari (Latur) earthquake (Mw 6.2) was a classic Stable Continental Region (SCR) intraplate earthquake. Occurring within the stable Peninsular Indian shield (previously considered seismically quiescent), it prompted a comprehensive revision of India's seismic zonation map.
8ID: GK-DMGT-00304
hardEarthquake Seismic Zones, BIS Codes & Tsunamis
Which Indian seismic zone encompassed the epicentre of the January 26, 2001 earthquake (Mw 7.7) that struck the Kachchh region of Gujarat?
Verified Explanation
The epicentre of the 2001 Bhuj earthquake (Mw 7.7 near Chobari, Bhachau taluka) lies squarely in Seismic Zone V, the highest hazard zone. The Kachchh rift basin is an active intraplate fault system characterized by major faults such as the Kutch Mainland Fault (KMF) and Katrol Hill Fault.
9ID: GK-DMGT-00305
hardEarthquake Seismic Zones, BIS Codes & Tsunamis
Which BIS standard establishes guidelines for earthquake-resistant design and construction of masonry and earthen buildings in India?
Verified Explanation
IS 4326: 2013 is the Bureau of Indian Standards code for 'Earthquake Resistant Design and Construction of Buildings'. It provides engineering detailing for masonry structures, timber construction, plinth bands, lintel bands, roof bands, and vertical reinforcement at corners and jambs.
10ID: GK-DMGT-00295
easyEarthquake Seismic Zones, BIS Codes & Tsunamis
What soil mechanics phenomenon occurs during earthquake shaking when saturated, loosely packed granular soil temporarily loses its shear strength and behaves like a liquid?
Verified Explanation
Soil liquefaction occurs when saturated loose cohesionless sandy soils experience cyclic seismic shaking, leading to an increase in pore water pressure and sudden loss of effective shear strength. This causes heavy structural settlement, foundation tilting, and sand boils during major earthquakes.