Question

most earthquakes are the result of movement along which of the following features (surfaces)?

foci
volcanoes
joints
epicenter
faults

question 7
2 pts
describe how sand volcanoes form.

sand volcanoes form when loose sediments slide downslope on a relatively slippery clay layer during an earthquake
an opening in the surface that ejects water and sand, but is not caused by earthquake activity.
an earthquake causes fractures to form, creating conduits for geothermal waters to erupt as geysers at the surface.
an earthquake causes loose, saturated sandy material to liquefy, shoot upward through fractures of a confining unit, and eventually erupt at the surface.

Explanation:

• For the first question:
• Foci: The focus (plural foci) is the point within the Earth where an earthquake rupture starts. It is not a surface - related feature for earthquake movement.
• Volcanoes: Volcanoes are related to magma movement and eruption. While there can be some seismic activity associated with volcanoes, most earthquakes are not due to movement along volcanoes.
• Joints: Joints are fractures in rocks where there has been no significant displacement. Earthquakes involve significant displacement, so joints are not the main feature.
• Epicenter: The epicenter is the point on the Earth's surface directly above the focus. It is not a surface along which movement occurs to cause an earthquake.
• Faults: Faults are fractures along which there has been significant displacement. Most earthquakes are the result of movement (sudden release of energy) along faults.
• For the second question:
• Option 1: Sand volcanoes (also known as sand boils) are not formed by sediment sliding on a clay layer. This description is more related to landslides.
• Option 2: Sand volcanoes are caused by earthquake activity. So, this option is incorrect.
• Option 3: Geothermal water eruptions as geysers are not sand volcanoes. Sand volcanoes are related to liquefaction.
• Option 4: During an earthquake, loose, saturated sandy material can liquefy (turn into a liquid - like state). The liquefied sand can then shoot upward through fractures in a confining unit and erupt at the surface, forming sand volcanoes.

Answer:

• First question: faults
• Second question: An earthquake causes loose, saturated sandy material to liquefy, shoot upward through fractures of a confining unit, and eventually erupt at the surface.