What does the beach ball diagram describe?
A focal mechanism, or “beachball”, is a graphic symbol that indicates the type of slip that occurs during an earthquake: strike-slip, normal, thrust (reverse), or some combination. It also shows the orientation of the fault that slipped.
What does the dark part of the beach ball diagram represent?
The quadrants are then colored, with black used for the compressional or up quadrants. For a map display of many faults, the black quadrants can be color coded by depth of the focus or the the magnitude. The two great circles represent the nodal planes for the earthquake.
What do moment tensor beach ball diagrams describe?
About Moment Tensors and “Beach Balls” A seismic moment tensor is a mathematical description of the forces that drive earthquake rupture, and they can be interpreted in terms of the nature of the faulting.
What are normal faults?
Normal, or Dip-slip, faults are inclined fractures where the blocks have mostly shifted vertically. If the rock mass above an inclined fault moves down, the fault is termed normal, whereas if the rock above the fault moves up, the fault is termed a Reverse fault.
What are 3 types of faults?
There are three main types of fault which can cause earthquakes: normal, reverse (thrust) and strike-slip. Figure 1 shows the types of faults that can cause earthquakes. Figures 2 and 3 show the location of large earthquakes over the past few decades.
What are the 4 main types of faults?
There are four types of faulting — normal, reverse, strike-slip, and oblique. A normal fault is one in which the rocks above the fault plane, or hanging wall, move down relative to the rocks below the fault plane, or footwall. A reverse fault is one in which the hanging wall moves up relative to the footwall.
What is rock faulting?
A fault is a fracture or zone of fractures between two blocks of rock. Faults allow the blocks to move relative to each other. Earth scientists use the angle of the fault with respect to the surface (known as the dip) and the direction of slip along the fault to classify faults.
What is a crack in the earth called?
Faults are cracks in the earth’s crust along which there is movement. These can be massive (the boundaries between the tectonic plates themselves) or very small.
How is the moment tensor decomposed in the beach ball diagram?
Even with the beach ball diagram, it can still be hard to interpret the geological or physical mechanism of the event. This is why the moment tensor is often decomposed into its constituent elementary source mechanisms. To decompose the moment tensor, the matrix is rotated to zero the off-diagonal elements.
How do you determine the size of a beach ball?
The easiest way to determine your beach ball will be the size you want, is to review the Inflated Size or Diameter of the Beach Balls we have listed. In the plant, the beach ball will loose some length at each end. They do this so when inflated, the ball is round and not egg shaped.
What does the center of the Beachball plot look like?
The center of the beachball plot is white for normal- fault mechanisms (a), and the center is black for reverse-fault mechanisms (b). Reverse-fault FMS diagrams look like my cat’s eyes. Oblique-slip faults have both strike-slip and dip-slip components.
When does a beachball plot have a normal component of slip?
If the center of the beachball plot is in a white quadrant (a), the fault has a normal component of slip, regardless of which of the two nodal planes is the fault; if the center is in a black quadrant (b), the fault has a reverse component of slip. Practice with basic interpretation Some FMS beachball diagrams are presented below.