In physical geography, which of the following is not considered a major causative factor for the origin of earthquakes?

Introduction / Context:
Earthquakes are sudden shakings of the earth crust that occur due to various geological processes. Competitive exams often ask which processes cause earthquakes and which do not. This question checks whether you can distinguish between primary causes of earthquakes and secondary effects such as the waves that travel after an earthquake has begun.

Given Data / Assumptions:

• The question asks for a factor that is not causative, meaning it does not originate an earthquake.
• Options include volcanic activity, isostatic adjustment, tectonic movements, and waves in rocks.
• We assume basic knowledge of plate tectonics and crustal processes.

Concept / Approach:
Most natural earthquakes occur because of stress buildup and sudden release along faults in the earth crust due to plate tectonics. Some earthquakes are associated with volcanic eruptions or isostatic adjustments as the crust responds to loading and unloading. However, seismic waves are not a cause of earthquakes; they are the vibrations that travel outward after an earthquake has started. Therefore, waves in rocks are an effect, not a cause. The correct choice must be the one that is clearly a result rather than an initiating process.

Step-by-Step Solution:
Step 1: Consider volcanic activity. Rising magma and explosive eruptions can fracture rocks and cause volcanic earthquakes, so volcanoes are genuine causative factors. Step 2: Consider isostatic adjustment. When ice sheets melt or sediments are removed, the crust slowly adjusts, and this stress readjustment can trigger earthquakes in some regions. Step 3: Consider tectonic movements. Movement of plates, subduction, collision, and transform motion directly create stress along faults, which is the main cause of most earthquakes worldwide. Step 4: Now look at waves in rocks. Seismic waves are produced after energy is suddenly released during an earthquake. They transmit the shaking but do not initiate the event. Step 5: Therefore, propagation of waves through rocks is not a causative factor; it is an effect of the earthquake source.

Verification / Alternative check:
Textbooks on seismology define the focus as the point where an earthquake starts and seismic waves as the vibrations that radiate from that focus. The processes that can create a focus include plate motions, volcanic intrusions, and isostatic changes. No standard reference lists seismic waves as a cause; they are always described as the result of stress release. This confirms that waves cannot be a primary cause of earthquakes.

Why Other Options Are Wrong:

• Volcanic activity: Movement of magma and eruption forces can crack rocks and generate earthquakes, especially in volcanic zones.
• Isostatic adjustment of the crust: Changes in weight on the crust cause vertical movements and can trigger intraplate earthquakes.
• Tectonic movements of plates: This is the dominant global cause of earthquakes along plate boundaries.

Common Pitfalls:
Learners sometimes confuse cause and effect, thinking that because waves are associated with earthquakes they must also cause them. Another confusion comes from the use of the term seismic waves in both descriptions of earthquakes and in general discussions of crustal behaviour. To avoid this, always separate the physical process that initiates the rupture (tectonics, volcanoes, isostatic changes) from the vibrations that simply transmit the energy (waves).

Final Answer:
The factor that is not a primary cause of earthquakes is propagation of waves through rocks.