Trend and Plunge : Gores Garis Pada Sesar

Summary

The video follows a geology fieldwork session where a geologist demonstrates measuring techniques for geological structures such as strike and dip on rock formations. Using a compass and level, they describe how to determine the orientation and angle of slickensides on a fault plane and calculate the strike and dip angles. The video covers various field tools, procedures, and methods essential for structural geology, giving a practical look at measuring fault orientations in situ. This session is located near Bandung, Indonesia, and references the Citarum formation as part of the geological analysis.

Takeaways

• 🧭 The speaker encounters mineral rocks and volcanoes in a field location and aims to measure a fault line structure.
• 🗺️ They are using a geological map of the Bandung area from the Citarum formation as a reference for their work.
• 📏 The primary goal is to measure the strike and dip of a fault plane using a compass tool.
• 📐 The first step is setting the compass to measure the strike, aligning it to ensure accuracy.
• 💧 The water level (watermaster) on the compass must be centered to correctly measure the strike.
• 🧭 The strike of the fault plane is measured at 175°, indicating the direction of the plane.
• 📉 Next, they measure the dip of the plane, which involves finding the perpendicular angle to the strike.
• 🧮 The dip is recorded at 55°, showing the angle of inclination of the fault plane.
• 🧱 The speaker discusses the formation of slickensides, which are caused by the movement of two rock surfaces against each other.
• 📊 The final measurements for the fault plane are a strike of 175° and a dip of 55°, providing detailed orientation information.

Q & A

What is the significance of slickenside in the script?

Slickenside refers to the polished surface of a fault plane caused by frictional movement. In the script, it is mentioned as an important feature observed in the field, which helps in identifying the direction of fault movement.

What are Strike and Dip as described in the script?

Strike refers to the direction of the horizontal line along a fault plane, while Dip is the angle at which the fault plane is inclined from the horizontal. These measurements are crucial for understanding the orientation of geological structures.

How is the Strike measured in the script?

The Strike is measured by aligning a compass with the fault surface, ensuring the bubble in the waterpass (spirit level) is centered, and reading the bearing of the fault line, which was approximately 175° in the demonstration.

What method is used to measure the Dip in the field?

The Dip is measured by holding the compass perpendicular to the fault plane and adjusting until the waterpass is level. The angle is then read from the compass, which showed 55° in the example given.

Why is consistency important when measuring Strike and Dip?

Consistency ensures that measurements are reliable and comparable across different parts of the fault or between different researchers. In the script, it emphasizes maintaining the same technique for accurate results.

What role does the waterpass (spirit level) play in the measurements?

The waterpass is used to ensure the compass is level when measuring both Strike and Dip. This helps in getting accurate readings by ensuring the instrument is correctly oriented relative to the fault plane.

What is the purpose of measuring both Strike and Dip in the field?

Measuring both Strike and Dip allows geologists to understand the orientation and movement along a fault or geological structure. This information is essential for mapping and analyzing tectonic activities.

What is meant by 'trend' in the context of the script?

The 'trend' refers to the direction in which a geological feature or fault line extends. It is usually measured as an azimuth or compass direction, and in this script, a trend of around 215° is mentioned.

What is the significance of the 45° dip angle mentioned at the end?

The 45° dip angle mentioned in the final example suggests a moderate incline of the fault plane, which is typical for many faults and can indicate the amount of vertical displacement along the fault.

How does the script demonstrate the process of fault line measurement?

The script provides a step-by-step guide for using a compass and waterpass to measure the Strike and Dip of a fault. It demonstrates the practical application of fieldwork techniques used by geologists.