Event (geomagnetic) - Event

Japanese: イベント（地磁気） - いべんと

...they are broadly divided into two periods (first, second, and third periods), named after experts in geomagnetic research: Brunhes, Matsuyama, Gauss, and Gilbert, from the most recent to the most recent. Between these periods are periods of reversal lasting less than 100,000 to 200,000 years, called events. The Brunhes period of the current geomagnetic field began about 700,000 years ago, and several events have been discovered, including one named "Biwa" (Biwa) because it was first discovered in the sediments of Lake Biwa.

From [Geomagnetic Chronology]

...This change between normal and reverse about 700,000 years ago is called the Matsuyama-Brunhes boundary, and is often used as a key to chronology. The period includes a period of reversal less than 100,000 to 200,000 years ago, called an event. The reverse Matsuyama period includes the normal events of Jaramillo and Olduvai, which are also key to determining the age.

*Some of the terminology explanations that mention "Event (Geomagnetic)" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

Japanese:

…逆方向)に大別され，新しい方からブリュンヌ，松山，ガウス，ギルバートと地磁気研究の大家の名がつけられている。これらの期の間には，10万～20万年以下の反転していた時期が含まれており，イベントという。現在の地磁気方向のブリュンヌ期は約70万年前からで，いくつかのイベントも発見されており，琵琶湖の堆積物から最初に発見されたので〈ビワ〉という名のイベントもある。…