The significance of apparent dip in geological cross-sections

Geologists use strike and dip measurements to generate realistic geologic maps and cross-sections by determining the attitude of rock strata or other planar geologic features. Data on rock attitudes, for example, aids in the identification of fold structures in layered rocks.

Any dip measured in a vertical plane that is not perpendicular to the strike line is referred to as an apparent dip. If you know the strike, you can calculate the true dip from the apparent dip using trigonometry. When geologic cross sections are produced at an angle that is not perpendicular to the strike, the apparent dip is used.

The apparent dip is determined by the angle formed by the cross-section and strike. If this angle is 90 degrees (perpendicular), the dip is true. The apparent dip will be shorter than the true dip if the angle between the strike line and the cross-section line is less than 90 degrees.

A: The plane is seen in a cross-section which is cut perpendicular to the strike of the plane

B: The plane is seen in a cross-section which is at some random angle to the strike of the plane

If a cross-section line is perpendicular to strike, the bed shown dipping in that cross-section is inclined at the real dip angle, which is the dip equal to the plane's steepest slope. Because dip is perpendicular to strike and strike lines are horizontal, the dip is perpendicular to strike. This is the apparent dip if the line of cross-section cuts through the Earth in a different way (not perpendicular to strike) and depicts the inclined strata as if they had a smaller dip.

Cross-sections through the soil, whether natural or man-made (e.g., cliffs, quarry faces, road cuttings, etc.), are unlikely to be parallel to the true dip. If these cross-sections are not perpendicular to strike, the true dip can be calculated by measuring strike and apparent dip.

The line of the section in the preceding figure is at an angle to strike. To calculate the apparent dip of the bed in the cross-section, we need two things: the correct orientation of the plane (strike, dip, and direction) and the angle between the strike and the cross-section. In the figure, the strike is E-W (090), and the real dip is:

tan−1(100′/500′) = 11.3◦

Let’s say β= 30◦ off the map.

Use the formula:

tan(α) = tan(δ) * cos(β)

Where α= apparent dip, δ= true dip, and β= angle between strike and cross-section line.

We can rearrange this equation to find the value you're looking for. Use the following formula to solve for in the preceding example, where we know and want to depict that bedding plane accurately in the cross-section we're drawing:

α=tan−1[tan(δ)∗tan(β)]

As an example, in our case:

α=tan−1[tan(11.3◦)∗tan(30◦)]

α= 9.8◦

This is the dip in our cross-section that you will be plotting.

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पर बाट देशलाई हेर्दा।

परदेश बाट देशलाई हेर्दा। हाम्रो आफ्नै भुगोल छ। भाषा छ। आफ्नै धर्म छ। देवता छ्न आफ्नै। नभएको त बुझाइ मात्र हो। आफ्नै इतिहास छ। भित्तामा आफ्नै पात्रो छ। गति आफ्नै छ। नभएको त गति तिब्र मात्र हो। सन्सार हेर्नलाई सगरमाथा छ। फेर्नको लागि सफा हावा छ। अन्नको लागि तराइको फाट छ। भिमकाय पहाड छ्न, खानी छ, मुलको पानी छ नहुनु पर्ने चाँइ हैरानी मात्र हो। आफ्नै गित छ्न संगीत छ्न। गायक छ्न गायिका छ्न। चलचित्र पनि आफ्नै छ्न। हिरो छ्न, हिरोईन छ्न। खड्किन थालेको चाइ आफ्नै कथा हो। हामी सग के छैन? हामीसग हिड्नलाई बाटो छ। पुरानो सभ्यताको पाटो छ। आफैले आर्जेको देशको माटो छ। नहुन पर्ने चाइ जात-धर्मको नाउँमा फाटो हो। हेर्ने हो भने हामी सग पहिला नै धेरै कुरा छ्न। बिधुतको लागि खोला-नदि छ्न। पर्यटनको लागि सुन्दर प्रकृति छ। सन्तुलित हावा पानी छ। न बनाय हुने भनेको दुत्सित मात्र हो। बिद्यालय छ्न। बिश्वबिद्धालय छ्न। बिध्या पिठ छ्न। बिद्यार्थी छ्न( अहिले सम्म) खड्किएको भनेको देशलाइ चाहिने पाठ्यक्रम र पठन पाठन हो। सानो भूगोल भैकन पनि हाम्रो देश सग धेरै कुरा छ। हिमाल छ। हिमालमा हिउँ छ( अहिले सम्म) सबै हिमाल विशाल छ्न।

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