(a) Discuss the intensity and magnitude scale commonly used to assess seismic damage. Write a note on the global distribution…

Seismic hazard is assessed by separating the size of the earthquake from the damage it produces. Magnitude and intensity. Magnitude is a base-10 logarithmic measure of earthquake size, not directly kinetic energy. Richter local magnitude (M_L) is based on maximum amplitude of recorded waves, while moment magnitude (M_w) is based on seismic moment, i.e. fault area × slip × rigidity; energy released is estimated from magnitude through empirical relations, with each unit increase implying about tenfold amplitude and 31.6-fold energy. Intensity scales, such as Modified Mercalli and MSK-64, use Roman numerals to describe observed shaking, structural damage, and human effects at a place; they are site-specific and therefore more useful for damage assessment.

Global distribution. Earthquakes are concentrated along plate boundaries. The Circum-Pacific belt, the Alpide or Mediterranean-Himalayan belt, and the Mid-oceanic ridge system contain most seismicity. The Circum-Pacific belt has the highest frequency and largest magnitudes due to oceanic plate subduction; the Alpide belt includes the Himalaya and is linked to India-Eurasia collision; mid-oceanic ridges have shallow, smaller events. Intraplate earthquakes are rare but important in India, where the Indian plate's collision with Eurasia and inherited crustal weaknesses control seismicity.

Seismic zones of India. IS 1893 (Part 1): 2016 divides India into Zones II–V. On the given map, mark Zone V as narrow, discontinuous high-risk bands along specified parts of J&K and Ladakh, the high Himalayan parts of Himachal Pradesh and Uttarakhand, Sikkim, North Bihar, most of the Northeast, Andaman & Nicobar, and Kutch; mark Zone IV in adjacent parts of Himachal Pradesh, Uttarakhand, Ladakh, and the Koyna-Warna region; mark Zone III in Punjab, Kerala, Latur, parts of Uttar Pradesh, Madhya Pradesh and Maharashtra; and mark Zone II in the remaining Deccan and low-risk areas. Zone V is not a continuous state-wide area; Ladakh is mostly Zone IV except specified Zone V parts. Zone IV surrounds Zone V in the Himalayan arc. Zone V includes parts of Kashmir and Assam; 2001 Bhuj occurred in Kutch, while the 2015 Nepal-Gorkha earthquake caused high intensities across Nepal and northern India.

Davis and Penck. Davis’s geomorphic cycle links erosion to a base level and a graded profile. In youth, relief is high and drainage is immature; in maturity, slopes are subdued and valleys widen; in old age, a peneplain forms. Uplift can renew the cycle. Its criticisms are that it assumes static uplift, is time-dependent rather than process-based, and treats stages as universal. Penck’s model emphasizes simultaneous crustal movement and erosion, with slopes retreating in parallel and development waxing and waning. It focuses on slope forms and endogenetic-exogenetic interaction rather than fixed stages.

Contours. Contours are lines joining points of equal elevation; the contour interval is the vertical difference between successive lines, and horizontal equivalent is the horizontal ground distance between successive contours. The interval is chosen according to map scale and relief; a small interval gives detailed relief, while a large interval generalizes it. A neat diagram of concentric closed contours shows a hill, while hachured closed contours show a depression. V-shaped contours pointing upstream indicate valleys; U-shaped contours radiating from a summit indicate spurs. Closely spaced contours show steep slopes, widely spaced contours gentle slopes; overlapping contours indicate cliffs. Ridge lines appear as contours bending around high ground, saddles as a dip between two high points, terraces as flat contour bands, and alluvial fans as fan-shaped spacing; drainage patterns follow the V-contours. In the diagrams, label the stream in the V, the summit in closed contours, and the cliff where contours merge. Thus, seismic scales, zonation, landform cycles, and contour reading together link tectonic forces with surface form and hazard.