US regulators activated "circuit breakers" in stocks designed to limit losses for the NY Stock Exchange & NASDAQ. Both exchanges were set to open with 5% losses this morning, as investors continue to hoard cash. The market sell-off is global, with Japan's stock Nikkei Index down over 5.6% and the German DAX down nearly 8% on the day. Margin calls are forcing the liquidation of many bellwether stocks to cover losses in other areas, creating a vicious cycle of selling.
As of Friday last week, over 20% of market positions held by institutional investors (banks, hedge funds, pension funds etc) were based on margin - money borrowed to purchase stocks or futures positions, with other stocks pledged as collateral. As stocks begin to decline, the lenders (typically large investment banks or stock brokerages) make a margin call, which automatically forces the sale of the stocks that are the collateral for the loan, to cover the losses of the stocks purchased by the loan.
This forced-selling leads to further stock market declines, and then even more stocks must be sold to cover other stocks held on margin - that is, stocks which had been purchased via loans that must now be paid back. Investment banks typically accept only higher-quality assets and stocks as collateral: Bellwether stocks such as the DOW Jones, Fortune 100 type companies, or other "safe" assets such as gold, silver, even commodities like oil and natural gas, etc.
All assets seem to decline at once, but much of it is because algorithms are causing the forced sale of assets to cover the 20% of the market that was purchased based on margin loans, which now need to be covered.