Well, it's turning into a nightmare of a week for ASX investors. As it currently stands, the S&P/ASX 200 Index (ASX: XJO) is on its fourth day of losses in a row, with many ASX 200 shares plunging in value this Thursday.

At the time of writing, the ASX 200 Index has crashed 1.4% lower, putting the index at just 8,300 points. It's a far cry from the new all-time high of 8,615.2 points that we saw only last Friday.

The ASX 200 has now recorded a drop every trading day this week thus far. Unless there is a dramatic turnaround, it looks as though today will continue that trend. As it currently stands, the market has fallen by a nasty 2.9% since Friday's close. It's now sitting at a new five-week low.

So why are ASX 200 shares taking such a dramatic tumble this Thursday?

Why are ASX 200 shares in freefall today?

Well, it was always going to be a tough day for ASX shares. As my Fool colleague noted this morning, investors were already expecting a 0.6% drop when the market opened.

But things seemed to get a lot worse when the latest employment numbers came out.

The Australian Bureau of Statistics (ABS) released its latest employment figures this morning. They showed the unemployment rate in the Australian economy ticking up by 0.1% to 4.1% over the month of January.

However, this figure was driven by an increase in workforce participation (remember, the unemployment rate only counts those actively looking for work). Breaking the numbers down reveals that employment rose by 44,000 jobs in January, with the number of unemployed people only rising by 23,000.

Despite the headline rate, the report reveals that the labour market is tightening. This is bad news for the share market because better unemployment figures mean that the Reserve Bank of Australia (RBA) will probably be more cautious about cutting interest rates in the coming months.

Earnings weigh on the market

Several earnings reports might also be helping to convince investors to hit the sell button today. This Thursday has seen ASX 200 shares ranging from ANZ Group Holdings Ltd (ASX: ANZ) and Magellan Financial Group Ltd (ASX: MFG) to Wesfarmers Ltd (ASX: WES) and Telstra Group Ltd (ASX: TLS) report their latest numbers.

Wesfarmers and Telstra put up some good numbers. As a result, their share prices are rising. However, we've seen big falls from even more ASX 200 shares. These include ANZ and Magellan, as well as Super Retail Group Ltd (ASX: SUL), Rio Tinto Ltd (ASX: RIO), and Fortescue Ltd (ASX: FMG).

As such, we can probably conclude that earnings are a net negative for the broader market today.

Despite this week's carnage, the ASX 200 index remains in positive territory for the year to date, currently sitting on a 1.25% rise. That extends to 8.4% over the past 12 months.