NEW YORK (Reuters) -Earnings reports next week, including from Tesla and Netflix, will provide a deeper look at U.S. corporate profits while delayed U.S. inflation data will mark another test of the stock market, which has become shakier even as it remains around record highs.

The fourth year of the S&P 500's bull run kicked off this week with some significant gyrations after a long period of market calm.

Revived U.S.-China trade tensions and credit concerns at regional U.S. banks drove the anxiety. The CBOE market volatility index, known as Wall Street's "fear gauge", has surged in recent days and hit its highest level in nearly six months on Friday.

"The market is becoming more volatile, but it's also coming off of a very non-volatile period where we didn't have a lot of risk catalysts bubbling to the top," said Michael Reynolds, vice president of investment strategy at Glenmede.

"Once you have valuations hit sort of full levels, as we're seeing now almost across the board, you have to be on the lookout for incremental risk catalysts."

The spark for the latest volatility was a surprise resurgence in U.S.-China trade tensions. Stocks slumped late last week after the U.S. threatened to significantly hike tariffs by November 1 over China's rare-earth export controls.

The U.S.-China trade issue will be key for markets in the coming week, said Doug Beath, global equity strategist at Wells Fargo Investment Institute. U.S. President Donald Trump confirmed on Friday that he would meet with Chinese President Xi Jinping in two weeks in South Korea.

Sharp swings in global financial shares to end the week also kept investors on edge as they weighed the extent of credit concerns emerging from regional U.S. banks.

Major stock indexes posted weekly gains and are on pace for strong years. The benchmark S&P 500 is up 13.3% year-to-date and 1.3% below its record high. But there are signs the market is weakening under the surface.

The percentage of S&P 500 stocks in some form of an uptrend declined from 77% in early July to 57% as of Tuesday while the number of stocks in a downtrend increased from 23% to 44% over that time, according to Adam Turnquist, chief technical strategist for LPL Financial. 

That "narrowing gap highlights emerging cracks in the market's foundation," Turnquist said in written commentary. Similarly, Kevin Gordon, senior investment strategist at Charles Schwab, said he will be watching how broadly based the market's gains are going forward.

"If you have a fewer number of companies that are actually moving higher, but the indexes do move higher because of the megacaps, that's a really important divergence," Gordon said.

Attention will be on third-quarter earnings after major banks started the reporting season on a strong note. Aside from streaming giant Netflix and electric vehicle maker Tesla, other companies due to report in the coming week include consumer companies Procter & Gamble and Coca-Cola, aerospace and defense giant RTX and tech stalwart IBM.

The corporate results and executive comments will offer insight into the economy as the U.S. government shutdown has stopped economic data releases since October 1, including monthly employment data.

Corporate "reports and what companies say is really our best chance at assessing what the broader economic health is," Gordon said.

The government has said it will release the U.S. consumer price index for September on Friday, nine days late, saying the CPI data allows the Social Security Administration to meet deadlines for timely payment of benefits.

The CPI report, which is a closely watched inflation gauge, will be released days before the Federal Reserve's next monetary policy meeting on October 28-29. The U.S. central bank is widely expected to cut interest rates by a quarter percentage point again, after weakening jobs data prompted the Fed to lower rates last month for the first time this year.

"We'd really have to see something out of left field in terms of notable inflation pressures to knock the Fed off of a rate cut path at the October meeting," Glenmede's Reynolds said.