Earthquakes

According to United States Geological Survey (USGS)- “Earthquake waves or seismic waves are the vibrations that travels through the earth’s crust and mantle, caused by the sudden movement of rocks during an earthquake.”

Types of Earthquake waves –

• Body waves are seismic waves which travel through the earth’s interior and divided in to two types –

a) Primary Waves – These are compressional waves which travel through solid, liquid and gas .It causes ground compression and expansion.

b) Shear Waves -These are shear waves which travel only through solid materials.These are slower than primary waves.It causes ground deformation and shaking.

• Surface waves are seismic waves that travel along the earth’s surface and divided into two types-

a) Rayleigh waves- These are rolling waves and these are most destructive wabe type which causes ground motion in circular motion.

b) Love waves – These are horizontal waves which cause ground motion perpendicular to direction of travel.They are less destructive than Rayleigh waves.

Emergence of Shadow Zones – 

• Earthquake occurs and generation of seismic waves occurs (P,S Waves).
• Seismic waves travel through earth’s interior and along the surface.
• Waves interaction with Earth’s core , mantle, & crust.It will led to refraction, reflection, diffraction and absorption.
• Waves are blocked or significantly reduced in certain areas creating shadow zones –

a)P-Wave Shadow Zone (105° to 145 ° from epicenter).

b)S-Wave Shadow Zone (105° to 105° from epicenter).

Understanding these waves and shadow zones will help the scientists in studying earth’s internal structure , predicting earthquake behaviour and will improve their hazard assessment.

Earthquake hazards pose significant threats to human life, infrastructure and economic stability. Ground shaking, soil liquefaction, landslides, tsunamis and structural collapse can cause widespread destruction, injuries and fatalities, emphasizing the need for preparedness and mitigation strategies.

Public awareness significantly enhances community resilience to earthquake hazards in several ways-

1. Public awareness increases knowledge, enabling communities to prepare, mitigate and respond effectively, fostering resilience through informed decision making and proactive measures.
2. Public awareness driven emergency planning enhances community resilience by facilitating evacuation drills, emergency protocols and hazard mapping, reducing earthquake related risks.
3. Public awareness promotes safety measures like securing furniture, retrofitting buildings and storing emergency supplies, reducing earthquake related injuries and fatalities.
4. Public awareness reduces panic, enabling calm evacuation, swift response and efficient recovery efforts during earthquakes.
5. Public awareness fosters community cooperation, promoting mutual support, resource sharing and collective earthquake response efforts.
6. Public awareness enables faster recovery by streamlining relief efforts, restoring infrastructure and revitalizing local economies efficiently.
7. Public awareness reduces earthquake related anxiety through education, empowering communities to cope with uncertainty and traumatic stress.
8. Public awareness fosters community cohesion, strengthening social bonds, trust and collective support during earthquake crises.
9. Public awareness empowers communities through knowledge, skills and confidence, enhancing resilience and earthquake preparedness.

Strategies for public awareness include educational campaigns, drills, hazard mapping, social media outreach, community engagement, school programs and collaborations with local authorities, promoting earthquake preparedness and resilience.

India has four seismic zones Zone I (low intensity), Zone II (low to moderate), Zone III (moderate to high) and Zone V (high intensity). Zones III and V cover Himalayan regions, Gujarat and parts of Maharashtra requiring special building codes.

Building codes and regulations mitigate earthquake damage in seismic zones through –

1.  Seismic resistant design ensures buildings withstand earthquake forces through flexible structures, reinforced materials and impact absorbing systems.
2. Structural reinforcement utilizes steel rebar, fiber mesh and advanced materials to enhance building strength and durability.
3. Foundation requirements include deep foundations, piles and specialized systems to transfer seismic forces to stable ground.
4. Regular inspections ensure compliance with seismic codes, identifying vulnerabilities and prompting corrective actions beforehand.
5. Material quality standards specify strength, durability and resilience requirements for steel, concrete and other construction materials.
6. Non structural element securing ensures partitions, ceilings, facades and equipment are anchored to prevent earthquake induced displacement.
7. Fire resistance requirements ensure buildings withstand post earthquake fires, protecting occupants and neighboring structures from spread.
8. Earthquake resistant systems utilize seismic isolation, damping and energy dissipation technologies to reduce building vibrations and stress.
9. Emergency evacuation routes provide clear, accessible escape paths, ensuring safe egress during and after earthquakes.
10. Early warning systems detect seismic activity by alerting occupants seconds before earthquake impact, enabling timely evacuation.