Blockchain, based on the distributed ledger technology, provides immediate settlement of transactions of digital assets and direct ownership. Since settlement of transactions is immediate, the blockchain system requires an ultra short tenor interest rate curve that is always up-to-date. Today, many market-quoted rates are still accrued at the end of each trading day, typically with one day as the shortest tenor available. This paper develops an interbank money market model for the equilibrium interest rate of ultra short tenor and updated at an intraday level with automated adjustment for the event of a flash crash. Apart from facilitating trades settlement on blockchain, our research findings are vital for central banks' efforts in stabilizing the currencies during flash crashes. We show that during the flash crash on 15 January 2015 when the Swiss National Bank (SNB) dropped the floor of CHF 1.2 per EUR, the ultra short CHF interest rates should have been highly negative to incentivize market makers to provide liquidity during the sharp CHF appreciation and to neutralize the arbitrage activities that aggravated the crash.