. Describe the spatial and depth distribution of earthquakes at ocean ridges and ocean trenches.

Ocean ridges are underwater mountain ranges, formed by the process of seafloor spreading, where new oceanic crust is created through volcanic activity and gradually moves away from the ridge. On the other hand, ocean trenches are the deepest parts of the ocean, formed by the process of subduction, where one tectonic plate is forced under another, causing the oceanic crust to be destroyed and recycled back into the Earth's mantle.

At ocean ridges, earthquakes are shallow and occur primarily along the ridge axis, where new oceanic crust is being formed. The process of seafloor spreading involves the continuous and gradual movement of tectonic plates, resulting in the stretching and thinning of the lithosphere. This leads to the formation of fractures (faults) in the crust, and as the crust continues to move and spread, these faults generate earthquakes. The earthquakes at ocean ridges typically occur at shallow depths, usually less than 20 kilometers below the seafloor. The frequency of earthquakes decreases with increasing distance from the ridge axis, reflecting the decreasing tectonic activity.

Ocean trenches, being the sites of subduction, are associated with earthquakes of varying depths, ranging from shallow to deep. The subduction of the oceanic plate creates a zone of contact between the two tectonic plates, called the subduction interface or Wadati-Benioff zone. Earthquakes in ocean trenches occur as a result of the friction between the subducting and overriding plates, the bending and deformation of the subducting plate, and the release of fluids and minerals during the process of subduction. The Wadati-Benioff zone can extend from the trench to depths of more than 600 kilometers. Shallow earthquakes, occurring at depths of less than 70 kilometers, are associated with the friction between the two plates near the trench. Intermediate-depth earthquakes, occurring at depths between 70 and 300 kilometers, are related to the deformation of the subducting slab as it descends into the mantle. Deep earthquakes, occurring at depths greater than 300 kilometers, are caused by the release of fluids and minerals from the subducting plate, leading to changes in the mantle material, and generating earthquakes in the process. In summary:

1. Ocean ridges: - Earthquakes primarily along the ridge axis - Shallow depths (< 20 km) - Frequency decreases with increasing distance from the ridge axis 2. Ocean trenches: - Earthquakes of varying depths (shallow to deep) - Occur along the subduction interface (Wadati-Benioff zone) - Shallow earthquakes (< 70 km) near the trench, intermediate-depth (70-300 km) and deep earthquakes (> 300 km) with increasing depth of subduction