EARTHQUAKES AND TSUNAMI IN HAWAI‘I (GG103) ~50 years of Hawai‘i seismicity

A: earthquake occurs at 00:00:00 GMT B: earthquake occurs at 00:00:30 GMT Δt = 30 s → ΔD = 7 km s -1 x 30 s = 210 km ~200 km D = v x t, ΔD = Δv x Δt, but v is constant: 7 km s -1 so ΔD = v x Δt If an earthquake signal arrives at different times to two different seismometers, you can say how much closer the earthquake was to one seismometer relative to the other. All these points are 200 km closer to A than they are to B Map view

In reality, the earthquake is on a curved plane, not a curved line… …and the plane doesn’t extend up in the air, only into the ground The earthquake was somewhere on this curved plane Attempt at perspective view

There is a similar curved surface that can be drawn based on the difference between the arrival times between stations A and C. The earthquake was somewhere on this curved line

The earthquake was somewhere on all three of these curved lines simultaneously, i.e., where they intersect

Examples USGS

Same N-S fault, different slip direction Stein and Wysession, An Introduction to seismology, earthquakes and Earth structure

Energy and Polarity of “First Motions” Cox and Hart. Plate Tectonics – How it works.

Earthquake on a vertical plane Edited from Cox and Hart. Plate Tectonics – How it works.

Determination of nodal planes Cox and Hart. Plate Tectonics – How it works.

Spreading of the seismic wave Cox and Hart. Plate Tectonics – How it works.

Data on the surface, interpreted in 3D Cox and Hart. Plate Tectonics – How it works.

With a lot of recordings we can reconstruct faults with any orientations Cox and Hart. Plate Tectonics – How it works.

Fault types and “Beach Ball” plots USGS

Example Focal mechanism diagrams on mid-ocean ridges Stein and Wysession, An Introduction to seismology, earthquakes and Earth structure