Recently many people felt seismic tremors (earthquakes) in parts of Indonesia, India, Iran and Thailand. These tremors aroused curiosities among young minds like yours. Here we discuss what are these shocks? How they occur? And other similar question every Rock Traveler™ should know the answer to when they think about EARTHQUAKES!
What is an earthquake?
Earthquake is a sudden vibration of the earth’s surface followed by energy dissipation. It may /may not be violent. Fault lines are one of major areas where earthquakes occur. Rocks on both sides of these lines dislocate, and deform due to sudden release of energy which had accumulated over a long period of time. The energy travels through the earth in the form of waves that are referred to as seismic waves.
Seismic Waves are classified mainly into three categories viz. primary (“P”), secondary / transverse (“S”) and surface waves. Rigidity and density of the material, through which they pass, define their speed. P waves, also known as compressional waves, travel within the earth at the highest speed and arrive first at the surface with a bang. The P waves can travel through both liquid and solid. Then, shear/secondary waves traveling at right angle to the consequent earth vibration reach the surface. The S waves can pass through only solid material. Surface waves cause maximum vibrations and shake the earth surface.
Terminology
Distance between the source of quake and the surface exactly above that point is called focal depth. There are three types of earthquakes viz. deep (over 700 km), intermediate (70 – 300 km) and shallow (up to 70 km) depending on focal depth. A number of quakes’ source lies in upper mantle / crust. Focus refers to the point of origin of the first P wave with in the earth. Epicenter is a point on the surface of the earth in line with its focus within earth.
Causes and Distribution of Earthquakes
Besides movement along fault lines, volcanic activity can cause tremors. Fault is a fracture where two rock blocks break and dislocate. The length of fault can vary from a cm to thousands of kilometers. Even human activities including mine excavations, nuclear explosions, and reservoir filling can trigger tremors. The mid oceanic ridges, plate boundaries and fault zones are prone to earthquakes. When tectonic plates slide past each other, stress deforms the rocks. The accumulated stress is released in the form of tremors when it exceeds the withstanding capacity of rocks. Earthquakes also occur at convergent plate boundaries where two plates meet. A small percentage of earthquakes occur within plates as plates weaken at boundaries and keep moving inward to form interior of plates. Some of the well known earthquake zones of the world are along the Pacific Ocean; and in the Mediterranean region.
The Agate is a multicolored variety of a rock called Chalcedony. It is found in a variety of diverse colors and patterns, and no two Agates, just like Rock Travelers, are alike. The extraordinary beauty and uniqueness of an Agate remind us how valuable each persons experience and memories are and why becoming a Rock Traveler™s is so important – a unique signature of oneself along the journey of life. What will you leave behind and who will know you were there?
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Recently many people felt seismic tremors (earthquakes) in parts of Indonesia, India, Iran and Thailand. These tremors aroused curiosities among young minds like yours. Here we discuss what are these shocks? How they occur? And other similar question every Rock Traveler™ should know the answer to when they think about EARTHQUAKES!
Besides movement along fault lines, volcanic activity can cause tremors. Fault is a fracture where two rock blocks break and dislocate. The length of fault can vary from a cm to thousands of kilometers. Even human activities including mine excavations, nuclear explosions, and reservoir filling can trigger tremors. The mid oceanic ridges, plate boundaries and fault zones are prone to earthquakes. When tectonic plates slide past each other, stress deforms the rocks. The accumulated stress is released in the form of tremors when it exceeds the withstanding capacity of rocks. Earthquakes also occur at convergent plate boundaries where two plates meet. A small percentage of earthquakes occur within plates as plates weaken at boundaries and keep moving inward to form interior of plates. Some of the well known earthquake zones of the world are along the Pacific Ocean; and in the Mediterranean region. 
