• 7.3-magnitude quake prompts tsunami warning in New Zealand

    March 4 (UPI)LINKY -- A powerful earthquake off New Zealand on Thursday triggered a tsunami warning, scientists and officials said.

    The 7.3-magnitude quake struck about 90 miles east of the Bay of Plenty, in the Pacific Ocean off the country's eastern coastline, according to the U.S. Geological Survey. The epicenter was located about 260 miles southeast of Auckland.

    New Zealand's National Emergency Management Agency issued a tsunami warning that spanned from Cape Runway to Tolaga Bay and advised residents to evacuate.

    "Strong and unusual currents and unpredictable surges near the shore are expected in [these] areas," a message on the NEMA website said.

    "This means a threat to beach harbor, estuary and small boat activities."

    Emergency officials warned that the tsunami's first wave might not be its largest and said the alert could last for hours.

    NEMA said evacuation orders override COVID-19 restrictions in affected areas, and that residents should leave if advised to do so.

    Several aftershocks with magnitudes between 5.3 and 4.5 followed the earthquake, the USGS :

    Tectonic Summary
    The March 4, 2021 M 7.3 earthquake northeast of Gisborne, New Zealand occurred as the result of oblique reverse faulting at approximately 20 km depth near the plate boundary between the Pacific and Australia plates. Preliminary moment tensor solutions indicate that the earthquake likely occurred on either a north-east dipping reverse fault with oblique right-lateral strike slip motion, or on a south-east dipping reverse fault with oblique left-lateral strike slip motion. The Pacific plate begins its westward subduction beneath the Australia plate at the Kermadec and Hikurangi subduction zone trenches with a velocity of about 47 mm/yr. The location, depth, and faulting mechanisms associated with this earthquake indicate that the earthquake likely occurred within the subducted Pacific lithosphere very close to the oceanic trench between these two tectonic plates.

    While commonly plotted as points on maps, earthquakes of this size are more appropriately described as slip over a larger fault area. Oblique faulting events of the size of the March 4 earthquake are typically about 85x25km in size (length x width).

    The Australia-Pacific plate boundary region east of the North Island of New Zealand has a history of large earthquakes both along the plate boundary proper, within the subducting Pacific Plate, and in the overlying Australia plate. Seismic activity is especially high in the Kermadec Islands region to the north. Within 250 km of the March 4, 2021 event, four earthquakes of M 7 or greater have occurred in the past century, with the most recent being an M7.0 oblique normal faulting earthquake in September 2016. The March 4, 2021 earthquake occurred ~45 km east-southeast of the September 2016 normal faulting earthquake. There have been 29 earthquakes of M 6 or greater within 250 km of the March 4 earthquake over the same time period. Despite the subduction zone environment, previous earthquake mechanisms in the vicinity of the March 4 earthquake exhibit a diverse range of faulting styles including predominantly thrust motion, normal motion, and oblique strike slip motion.
    This article was originally published in forum thread: 7.3-magnitude quake prompts tsunami warning in New Zealand started by Photoboy View original post