Moment tensors provide depth control for reliable tsunami prediction

Seaquakes have the potential to generate destructive tsunamis when the magnitude is large, the earthquake occurs at shallow depth below the ocean floor and the earthquake mechanism has a significant uplift component. Their correct determination is therefore crucial for Tsunami Early Warning conducted in many centers worldwide. False as well as missed warnings may have large societal and economic impacts.

Reliable and unique estimation of magnitude, earthquake depth and mechanism, and the tsunami thread are feasible using SeisComP3 and gempa’s TOAST and MTV. The software modules together combine observations of earthquakes and tsunami wave heights with rapid modeling of earthquake sources and tsunami waves.

On 04 April 2016 a shallow M6.8 earthquake struck the Vanuatu region in the open sea. Without the correct determination of the earthquake moment tensor at the centroid depth using MTV the tsunami potential would have been overestimated giving rise to potentially higher tsunami wave heights. Using MTV, the moment tensor and the centroid depth were determined. By inversion for the moment tensor, the initial hypocenter was shifted from tsunami-hazardous depth of just 10 km to a centroid of 33 km. The shift in depth changes the tsunami prediction made by gempa’s TOAST from wave heights of about 0.3 m to less than 10 cm at the coasts of the Pacific Islands.

In this way, gempa’s TOAST and MTV have contributed to reliable Tsunami-Early warning for the countries of the Pacific Ocean. Both software modules are applied at data centers worldwide.

TOAST and Moment Tensors belong to the gempa product family . MTV is a joint development of gempa and GFZ Potsdam .

Using first arrivals from seismic P waves the earthquake epicentre was correctly determined but the depth seems to be shallow.

Using gempa’s MTV the seismic moment tensor is computed by inversion of waveforms.

The centroid depth of the earthquake was refined during inversion moving the earthquake from 10 to 33 km.

The centroid depth of the earthquake was refined during inversion moving the earthquake from 10 to 33 km.

The tsunami modeling by TOAST shows that small tsunami wave could have been generate by the shallower earthquake source at 10 km depth.

The TOAST modeling for 33 km centroid depth predicts only minor wave heights.

TOAST: Comparison with mariograms (sea-level mesurements) show that the TOAST-modeled tsunami heights for an earthquake depth of 33 km agree very well witht the observations.

TOAST: Comparison with mariograms (sea-level measurements) show that the TOAST-modeled tsunami heights for an earthquake depth of 33 km agree very well with the observations.